User’s Security Handbook -- RFC 2504 February 1999

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Network Working Group E. Guttman Request for Comments: 2504 Sun Microsystems FYI: 34 L. Leong Category: Informational COLT Internet

                                                             G. Malkin
                                                          Bay Networks
                                                         February 1999

                       Users' Security Handbook

Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (1999).  All Rights Reserved.


  The Users' Security Handbook is the companion to the Site Security
  Handbook (SSH).  It is intended to provide users with the information
  they need to help keep their networks and systems secure.

Table of Contents

  Part One: Introduction . . . . . . . . . . . . . . . . . . . .  2
  1.   READ.ME . . . . . . . . . . . . . . . . . . . . . . . . .  2
  2.   The Wires have Ears . . . . . . . . . . . . . . . . . . .  3
  Part Two: End-users in a centrally-administered network  . . .  4
  3.   Watch Out! . . . . . . . . . . . . . . . . . . . .  . . .  4
  3.1.   The Dangers of Downloading  . . . . . . . . . . . . . .  4
  3.2.   Don't Get Caught in the Web . . . . . . . . . . . . . .  5
  3.3.   Email Pitfalls  . . . . . . . . . . . . . . . . . . . .  6
  3.4.   Passwords . . . . . . . . . . . . . . . . . . . . . . .  7
  3.5.   Viruses and Other Illnesses . . . . . . . . . . . . . .  7
  3.6.   Modems  . . . . . . . . . . . . . . . . . . . . . . . .  8
  3.7.   Don't Leave Me... . . . . . . . . . . . . . . . . . . .  9
  3.8.   File Protections  . . . . . . . . . . . . . . . . . . .  9
  3.9.   Encrypt Everything  . . . . . . . . . . . . . . . . . . 10
  3.10.  Shred Everything Else . . . . . . . . . . . . . . . . . 10
  3.11.  What Program is This, Anyway? . . . . . . . . . . . . . 11
  4.   Paranoia is Good  . . . . . . . . . . . . . . . . . . . . 11
  Part Three: End-users self administering a networked computer  14
  5.   Make Your Own Security Policy . . . . . . . . . . . . . . 14

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RFC 2504 Users' Security Handbook February 1999

  6.   Bad Things Happen . . . . . . . . . . . . . . . . . . . . 15
  6.1.   How to Prepare for the Worst in Advance . . . . . . . . 15
  6.2.   What To Do if You Suspect Trouble . . . . . . . . . . . 16
  6.3.   Email . . . . . . . . . . . . . . . . . . . . . . . . . 17
  7.   Home Alone  . . . . . . . . . . . . . . . . . . . . . . . 17
  7.1.   Beware of Daemons . . . . . . . . . . . . . . . . . . . 17
  7.2.   Going Places  . . . . . . . . . . . . . . . . . . . . . 19
  7.3.   Secure It!  . . . . . . . . . . . . . . . . . . . . . . 20
  8.   A Final Note  . . . . . . . . . . . . . . . . . . . . . . 20
  Appendix: Glossary of Security Terms . . . . . . . . . . . . . 21
  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 31
  References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 32
  Full Copyright Statement . . . . . . . . . . . . . . . . . . . 33

Part One: Introduction

  This document provides guidance to the end-users of computer systems
  and networks about what they can do to keep their data and
  communication private, and their systems and networks secure. Part
  Two of this document concerns "corporate users" in small, medium and
  large corporate and campus sites.  Part Three of the document
  addresses users who administer their own computers, such as home
  System and network administrators may wish to use this document as
  the foundation of a site-specific users' security guide; however,
  they should consult the Site Security Handbook first [RFC2196].
  A glossary of terms is included in an appendix at the end of this
  document, introducing computer network security notions to those not
  familiar with them.


  Before getting connected to the Internet or any other public network,
  you should obtain the security policy of the site that you intend to
  use as your access provider, and read it.  A security policy is a
  formal statement of the rules by which users who are given access to
  a site's technology and information assets must abide.  As a user,
  you are obliged to follow the policy created by the decision makers
  and administrators at your site.
  A security policy exists to protect a site's hardware, software and
  data.  It explains what the security goals of the site are, what
  users can and cannot do, what to do and who to contact when problems
  arise, and generally informs users what the "rules of the game" are.

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2. The Wires have Ears

  It is a lot easier to eavesdrop on communications over data networks
  than to tap a telephone conversation.  Any link between computers may
  potentially be insecure, as can any of the computers through which
  data flows.  All information passing over networks may be
  eavesdropped on, even if you think "No one will care about this..."
  Information passing over a network may be read not only by the
  intended audience but can be read by others as well.  This can happen
  to personal Email and sensitive information that is accessed via file
  transfer or the Web.  Please refer to the "Don't Get Caught in the
  Web" and "Email Pitfalls" sections for specific information on
  protecting your privacy.
  As a user, your utmost concerns should, firstly, be to protect
  yourself against misuse of your computer account(s) and secondly, to
  protect your privacy.
  Unless precautions are taken, every time you log in over a network,
  to any network service, your password or confidential information may
  be stolen.  It may then be used to gain illicit access to systems you
  have access to.  In some cases, the consequences are obvious:  If
  someone gains access to your bank account, you might find yourself
  losing some cash, quickly.  What is not so obvious is that services
  which are not financial in nature may also be abused in rather costly
  ways.  You may be held responsible if your account is misused by
  someone else!
  Many network services involve remote log in.  A user is prompted for
  his or her account ID (ie. user name) and password.  If this
  information is sent through the network without encryption, the
  message can be intercepted and read by others.  This is not really an
  issue when you are logging in to a "dial-in" service where you make a
  connection via telephone and log in, say to an online service
  provider, as telephone lines are more difficult to eavesdrop on than
  Internet communications.
  The risk is there when you are using programs to log in over a
  network.  Many popular programs used to log in to services or to
  transfer files (such as telnet and ftp, respectively) send your user
  name and password and then your data over the network without
  encrypting them.
  The precaution commonly taken against password eavesdropping by
  larger institutions, such as corporations, is to use one-time
  password systems.

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  Until recently, it has been far too complicated and expensive for
  home systems and small businesses to employ secure log in systems.
  However, an increasing number of products enable this to be done
  without fancy hardware, using cryptographic techniques.  An example
  of such a technique is Secure Shell [SSH], which is both freely and
  commercially available for a variety of platforms.  Many products
  (including SSH-based ones) also allow data to be encrypted before it
  is passed over the network.

Part Two: End-users in a centrally-administered network

  The following rules of thumb provide a summary of the most important
  pieces of advice discussed in Part Two of this document:
   - Know who your security point-of-contact is.
   - Keep passwords secret at all times.
   - Use a password-locked screensaver or log out when you leave your
   - Don't let simply anyone have physical access to your computer or
     your network.
   - Be aware what software you run and very wary of software of
     unknown origin.  Think hard before you execute downloaded
   - Do not panic.  Consult your security point-of-contact, if
     possible, before spreading alarm.
   - Report security problems as soon as possible to your security

3. Watch Out!

3.1. The Dangers of Downloading

  An ever expanding wealth of free software has become available on the
  Internet.  While this exciting development is one of the most
  attractive aspects of using public networks, you should also exercise
  caution.  Some files may be dangerous.  Downloading poses the single
  greatest risk.
  Be careful to store all downloaded files so that you will remember
  their (possibly dubious) origin.  Do not, for example, mistake a
  downloaded program for another program just because they have the
  same name.  This is a common tactic to fool users into activating
  programs they believe to be familiar but could, in fact, be

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  Programs can use the network without making you aware of it.  One
  thing to keep in mind is that if a computer is connected, any program
  has the capability of using the network, with or without informing
  you.  Say, for example:
    You download a game program from an anonymous FTP server. This
    appears to be a shoot-em-up game, but unbeknownst to you, it
    transfers all your files, one by one, over the Internet to a
    cracker's machine!
  Many corporate environments explicitly prohibit the downloading and
  running of software from the Internet.

3.2. Don't Get Caught in the Web

  The greatest risk when web browsing is downloading files.  Web
  browsers allow any file to be retrieved from the Internet.  See "The
  Dangers of Downloading".
  Web browsers are downloading files even when it is not entirely
  obvious.  Thus, the risk posed by downloading files may be present
  even if you do not actively go out and retrieve files overtly.  Any
  file which you have loaded over the network should be considered
  possibly dangerous (even files in the web browser's cache).  Do not
  execute them by accident, as they may be malicious programs.
  (Remember, programs are files, too.  You may believe you have
  downloaded a text file, when in fact it is a Trojan Horse program,
  script, etc.)
  Web browsers may download and execute programs on your behalf, either
  automatically or after manual intervention.  You may disable these
  features.  If you leave them enabled, be sure that you understand the
  consequences.  You should read the security guide which accompanies
  your web browser as well as the security policy of your company.  You
  should be aware that downloaded programs may be risky to execute on
  your machine.  See "What program is this, anyway?".
  Web pages often include forms.  Be aware that, as with Email, data
  sent from a web browser to a web server is not secure.  Several
  mechanisms have been created to prevent this, most notably Secure
  Sockets Layer [SSL].  This facility has been built into many web
  browsers.  It encrypts data sent between the user's web browser and
  the web server so no one along the way can read it.
  It is possible that a web page will appear to be genuine, but is, in
  fact, a forgery.  It is easy to copy the appearance of a genuine web
  page and possible to subvert the network protocols which contact the
  desired web server, to misdirect a web browser to an imposter.

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  That threat may be guarded against using SSL to verify if a web page
  is genuine.  When a 'secure' page has been downloaded, the web
  browser's 'lock' or 'key' will indicate so.  It is good to
  double-check this: View the 'certificate' associated with the web
  page you have accessed.  Each web browser has a different way to do
  this.  The certificate will list the certificate's owner and who
  issued it.  If these look trustworthy, you are probably OK.

3.3 Email Pitfalls

  All the normal concerns apply to messages received via Email that you
  could receive any other way.  For example, the sender may not be who
  he or she claims to be.  If Email security software is not used, it
  is very difficult to determine for sure who sent a message.  This
  means that Email itself is a not a suitable way to conduct many types
  of business.  It is very easy to forge an Email message to make it
  appear to have come from anyone.
  Another security issue you should consider when using Email is
  privacy.  Email passes through the Internet from computer to
  computer.  As the message moves between computers, and indeed as it
  sits in a user's mailbox waiting to be read, it is potentially
  visible to others. For this reason, it is wise to think twice before
  sending confidential or extremely personal information via Email.
  You should never send credit card numbers and other sensitive data
  via unprotected Email.  Please refer to "The Wires Have Ears".
  To cope with this problem, there are privacy programs available, some
  of which are integrated into Email packages.
  One service many Email users like to use is Email forwarding.  This
  should be used very cautiously.  Imagine the following scenario:
     A user has an account with a private Internet Service Provider and
     wishes to receive all her Email there.  She sets it up so that her
     Email at work is forwarded to her private address.  All the Email
     she would receive at work then moves across the Internet until it
     reaches her private account.  All along the way, the Email is
     vulnerable to being read.  A sensitive Email message sent to her
     at work could be read by a network snoop at any of the many stops
     along the way the Email takes.
  Note that Email sent or received at work may not be private.  Check
  with your employer, as employers may (in some instances) legally both
  read your Email and make use of it.  The legal status of Email
  depends on the privacy of information laws in force in each country.

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  Many mail programs allow files to be included in Email messages.  The
  files which come by Email are files like any other.  Any way in which
  a file can find its way onto a computer is possibly dangerous.  If
  the attached file is merely a text message, fine.  But it may be more
  than a text message.  If the attached file is itself a program or an
  executable script, extreme caution should be applied before running
  it.  See the section entitled "The Dangers of Downloading".

3.4 Passwords

  Passwords may be easily guessed by an intruder unless precautions are
  taken.  Your password should contain a mixture of numbers, upper and
  lower case letters, and punctuation.  Avoid all real words in any
  language, or combinations of words, license plate numbers, names and
  so on.  The best password is a made-up sequence (e.g., an acronym
  from a phrase you won't forget), such as "2B*Rnot2B" (but don't use
  this password!).
  Resist the temptation to write your password down.  If you do, keep
  it with you until you remember it, then shred it!  NEVER leave a
  password taped onto a terminal or written on a whiteboard.  You
  wouldn't write your PIN code on your automated teller machine (ATM)
  card, would you?  You should have different passwords for different
  accounts, but not so many passwords that you can't remember them.
  You should change your passwords periodically.
  You should also NEVER save passwords in scripts or login procedures
  as these could be used by anyone who has access to your machine.
  Be certain that you are really logging into your system.  Just
  because a login prompt appears and asks you for your password does
  not mean you should enter it.  Avoid unusual login prompts and
  immediately report them to your security point-of-contact.  If you
  notice anything strange upon logging in, change your password.
  Unless precautions have been taken to encrypt your password when it
  is sent over the network, you should, if possible, use "one-time
  passwords" whenever you log in to a system over a network.  (Some
  applications take care of that for you.)  See "The Wires Have Ears"
  for more information on the risks associated with logging in over a

3.5 Viruses and Other Illnesses

  Viruses are essentially unwanted pieces of software that find their
  way onto a computer.  What the virus may do once it has entered its
  host, depends on several factors:  What has the virus been programmed
  to do?  What part of the computer system has the virus attacked?

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  Some viruses are 'time bombs' which activate only when given a
  particular condition, such as reaching a certain date.  Others remain
  latent in the system until a particular afflicted program is
  activated.  There are still others which are continually active,
  exploiting every opportunity to do mischief.  A subtle virus may
  simply modify a system's configuration, then hide.
  Be cautious about what software you install on your system.  Use
  software from "trusted sources", if possible.  Check your site policy
  before installing any software:  Some sites only allow administrators
  to install software to avoid security and system maintenance
  Centrally-administered sites have their own policy and tools for
  dealing with the threat of viruses.  Consult your site policy or find
  out from your systems administrator what the correct procedures are
  to stay virus free.
  You should report it if a virus detection tool indicates that your
  system has a problem.  You should notify your site's systems
  administrators as well as the person you believe passed the virus to
  you.  It is important to remain calm.  Virus scares may cause more
  delay and confusion than an actual virus outbreak.  Before announcing
  the virus widely, make sure you verify its presence using a virus
  detection tool, if possible, with the assistance of
  technically-competent personnel.
  Trojan Horse programs and worms are often categorized with viruses.
  Trojan Horse programs are dealt with in the "What Program is This,
  Anyway?" section.  For the purposes of this section, worms should be
  considered a type of virus.

3.6 Modems

  You should be careful when attaching anything to your computer, and
  especially any equipment which allows data to flow.  You should get
  permission before you connect anything to your computer in a
  centrally-administered computing environment.
  Modems present a special security risk.  Many networks are protected
  by a set of precautions designed to prevent a frontal assault from
  public networks.  If your computer is attached to such a network, you
  must exercise care when also using a modem.  It is quite possible to
  use the modem to connect to a remote network while *still* being
  connected to the 'secure' net.  Your computer can now act as a hole
  in your network's defenses.  Unauthorized users may be able to get
  onto your organization's network through your computer!

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  Be sure you know what you are doing if you leave a modem on and set
  up your computer to allow remote computers to dial in.  Be sure you
  use all available security features correctly.  Many modems answer
  calls by default.  You should turn auto-answer off unless you are
  prepared to have your computer respond to callers.  Some 'remote
  access' software requires this.  Be sure to turn on all the security
  features of your 'remote access' software before allowing your
  computer to be accessed by phone.
  Note that having an unlisted number will not protect you from someone
  breaking into your computer via a phone line.  It is very easy to
  probe many phone lines to detect modems and then launch attacks.

3.7 Don't Leave Me...

  Do not leave a terminal or computer logged in and walk away.  Use
  password-locked screensavers whenever possible.  These can be set up
  so that they activate after the computer has been idle for a while.
  Sinister as it may seem, someone coming around to erase your work is
  not uncommon.  If you remained logged in, anyone can come by and
  perform mischief for which you may be held accountable.  For example,
  imagine the trouble you could be in for if nasty Email were sent to
  the president of your company in your name, or your account were used
  to transfer illegal pornography.
  Anyone who can gain physical access to your computer can almost
  certainly break into it.  Therefore, be cautious regarding who you
  allow access to your machine.  If physically securing your machine is
  not possible, it is wise to encrypt your data files kept on your
  local hard disk.  If possible, it is also wise to lock the door to
  one's office where the computer is stored.

3.8 File Protections

  Data files and directories on shared systems or networked file
  systems require care and maintenance.  There are two categories of
  such systems:
   - Files to share
     Shared files may be visible to everyone or to a restricted group
     of other users.  Each system has a different way of specifying
     this.  Learn how to control sharing permissions of files and
     implement such control without fail.

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   - Protected files
     These include files that only you should have access to, but
     which are also available to anyone with system administrator
     privileges.  An example of this are files associated with the
     delivery of Email.  You don't want other users to read your Email,
     so make sure such files have all the necessary file permissions
     set accordingly.

3.9 Encrypt Everything

     Additionally, there are files that are private.  You may have files
     which you do not wish anyone else to have access to.  In this case,
     it is prudent to encrypt the file.  This way, even if your network is
     broken into or the systems administrator turns into Mr. Hyde, your
     confidential information will not be available.  Encryption is also
     very important if you share a computer.  For example, a home computer
     may be shared by room mates who are friends but prefer to keep their
     Email and financial information private.  Encryption allows for
     shared yet private usage.
     Before you encrypt files, you should check your site's security
     policy.  Some employers and countries expressly forbid or restrict
     the storing and/or transferring of encrypted files.
     Be careful with the passwords or keys you use to encrypt files.
     Locking them away safely not only helps to keep them from prying eyes
     but it will help you keep them secure too; for if you lose them, you
     will lose your ability to decrypt your data as well!  It may be wise
     to save more than one copy.  This may even be required, if your
     company has a key escrow policy, for example.  This protects against
     the possibility that the only person knowing a pass phrase may leave
     the company or be struck by lightning.
     Whilst encryption programs are readily available, it should be noted
     that the quality can vary widely.  PGP (which stands for "Pretty Good
     Privacy") for example, offers a strong encryption capability.  Many
     common software applications include the capability to encrypt data.
     The encryption facilities in these are typically very weak.
     You should not be intimidated by encryption software.  Easy-to-use
     software is being made available.

3.10 Shred Everything Else

     You would be surprised what gets thrown away into the waste-paper
     basket:  notes from meetings, old schedules, internal phone lists,
     computer program listings, correspondence with customers and even

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     market analyses.  All of these would be very valuable to competitors,
     recruiters and even an overzealous (hungry?) journalist looking for a
     scoop.  The threat of dumpster diving is real - take it seriously!
     Shred all potentially useful documents before discarding them.
     You should also be aware that deleting a file does not erase it in
     many cases.  The only way to be sure that an old hard disk does not
     contain valuable data may be to reformat it.

3.11 What Program is This, Anyway?

     Programs have become much more complex in recent years.  They are
     often extensible in ways which may be dangerous.  These extensions
     make applications more flexible, powerful and customizable.  They
     also open the end-user up to all sorts of risks.
   - A program may have "plug-in" modules.  You should not trust the
     plug-ins simply because you are used to trusting the programs
     they plug into.  For example: Some web pages suggest that the
     user download a plug-in to view or use some portion of the web
     page's content.  Consider: What is this plug-in?  Who wrote it?
     Is it safe to include it in your web browser?
   - Some files are "compound documents".  This means that instead of
     using one single program, it will be necessary to run several
     programs in order to view or edit a document.  Again, be careful
     of downloading application components.  Just because they
     integrate with products which are well-known does not mean that
     they can be trusted.  Say, you receive an Email message which can
     only be read if you download a special component.  This component
     could be a nasty program which wipes out your hard drive!
   - Some programs are downloaded automatically when accessing web
     pages.  While there are some safeguards to make sure that these
     programs may be used safely, there have been security flaws
     discovered in the past.  For this reason, some centrally-
     administered sites require that certain web browser capabilities
     be turned off.

4. Paranoia is Good

  Many people do not realize it, but social engineering is a tool which
  many intruders use to gain access to computer systems.  The general
  impression that people have of computer break-ins is that they are
  the result of technical flaws in computer systems which the intruders
  have exploited.  People also tend to think that break-ins are purely
  technical.  However, the truth is that social engineering plays a big

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  part in helping an attacker slip through security barriers.  This
  often proves to be an easy stepping-stone onto the protected system
  if the attacker has no authorized access to the system at all.
  Social engineering may be defined, in this context, as the act of
  gaining the trust of legitimate computer users to the point where
  they reveal system secrets or help someone, unintentionally, to gain
  unauthorized access to their system(s).  Using social engineering, an
  attacker may gain valuable information and/or assistance that could
  help break through security barriers with ease.  Skillful social
  engineers can appear to be genuine but are really full of deceit.
  Most of the time, attackers using social enginering work via
  telephone.  This not only provides a shield for the attacker by
  protecting his or her identity, it also makes the job easier because
  the attacker can claim to be a particular someone with more chances
  of getting away with it.
  There are several types of social engineering.  Here are a few
  examples of the more commonly-used ones:
   - An attacker may pretend to be a legitimate end-user who is new to
     the system or is simply not very good with computers.  This
     attacker may approach systems administrators and other end-users
     for help.  This "user" may have lost his password, or simply can't
     get logged into the system and needs to access the system
     urgently.  Attackers have also been known to identify themselves
     as some VIP in the company, screaming at administrators to get
     what they want.  In such cases, the administrator (or it could be
     an end-user) may feel threatened by the caller's authority and
     give in to the demands.
   - Attackers who operate via telephone calls may never even have seen
     the screen display on your system before.  In such cases, the
     trick attackers use is to make details vague, and get the user to
     reveal more information on the system.  The attacker may sound
     really lost so as to make the user feel that he is helping a
     damsel in distress.  Often, this makes people go out their way to
     help.  The user may then reveal secrets when he is off-guard.
   - An attacker may also take advantage of system problems that have
     come to his attention.  Offering help to a user is an effective
     way to gain the user's trust.  A user who is frustrated with
     problems he is facing will be more than happy when someone comes
     to offer some help.  The attacker may come disguised as the
     systems administrator or maintenance technician.  This attacker
     will often gain valuable information because the user thinks that
     it is alright to reveal secrets to technicians.  Site visits may

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     pose a greater risk to the attacker as he may not be able to make
     an easy and quick get-away, but the risk may bring fruitful
     returns if the attacker is allowed direct access to the system by
     the naive user.
   - Sometimes, attackers can gain access into a system without prior
     knowledge of any system secret nor terminal access.  In the same way
     that one should not carry someone else's bags through Customs, no user
     should key in commands on someone's behalf.  Beware of attackers who
     use users as their own remotely-controlled fingers to type commands on
     the user's keyboard that the user does not understand, commands which
     may harm the system.  These attackers will exploit system software
     bugs and loopholes even without direct access to the system.  The
     commands keyed in by the end-user may bring harm to the system, open
     his own account up for access to the attacker or create a hole to
     allow the attacker entry (at some later time) into the system.  If you
     are not sure of the commands you have been asked to key in, do not
     simply follow instructions.  You never know what and where these could
     lead to...
  To guard against becoming a victim of social engineering, one
  important thing to remember is that passwords are secret.  A password
  for your personal account should be known ONLY to you.  The systems
  administrators who need to do something to your account will not
  require your password.  As administrators, the privileges they have
  will allow them to carry out work on your account without the need
  for you to reveal your password.  An administrator should not have to
  ask you for your password.
  Users should guard the use of their accounts, and keep them for their
  own use.  Accounts should not be shared, not even temporarily with
  systems administrators or systems maintenance techinicians.  Most
  maintenance work will require special privileges which end-users are
  not given.  Systems administrators will have their own accounts to
  work with and will not need to access computer systems via an
  end-user's account.
  Systems maintenance technicians who come on site should be
  accompanied by the local site administrator (who should be known to
  you).  If the site administrator is not familiar to you, or if the
  technician comes alone, it is wise to give a call to your known site
  administrator to check if the technician should be there.  Yet, many
  people will not do this because it makes them look paranoid and it is
  embarrassing to show that they have no, or little trust in these

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  Unless you are very sure that the person you are speaking to is who he
  or she claims to be, no secret information should ever be revealed to
  such people.  Sometimes, attackers may even be good enough to make
  themselves sound like someone whose voice you know over the phone.  It
  is always good to double check the identity of the person.  If you are
  unable to do so, the wisest thing to do is not to reveal any secrets.
  If you are a systems administrator, there should be security
  procedures for assignment and reassignment of passwords to users, and
  you should follow such procedures.  If you are an end-user, there
  should not be any need for you to have to reveal system secrets to
  anyone else.  Some companies assign a common account to multiple
  users.  If you happen to be in such a group, make sure you know
  everyone in that group so you can tell if someone who claims to be in
  the group is genuine.

Part Three: End-users self administering a networked computer

  The home user or the user who administers his own network has many of
  the same concerns as a centrally-administered user.  The following is
  a summary of additional advice given in Part Three:
   - Read manuals to learn how to turn on security features, then turn
     them on.
   - Consider how private your data and Email need to be.  Have you
     invested in privacy software and learned how to use it yet?
   - Prepare for the worst in advance.
   - Keep yourself informed about what the newest threats are.

5. Make Your Own Security Policy

  You should decide ahead of time what risks are acceptable and then
  stick to this decision.  It is also wise to review your decision at
  regular intervals and whenever the need to do so arises.  It may be
  wise to simply avoid downloading any software from the network which
  comes from an unknown source to a computer storing business records,
  other valuable data and data which is potentially damaging if the
  information was lost or stolen.
  If the system has a mixed purpose, say recreation, correspondence
  and some home accounting, perhaps you will hazard some downloading of
  software.  You unavoidably take some risk of acquiring stuff
  which is not exactly what it seems to be.
  It may be worthwhile installing privacy software on a computer if it
  is shared by multiple users.  That way, a friend of a room mate won't
  have access to your private data, and so on.

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6. Bad Things Happen

  If you notice that your files have been modified or ascertain somehow
  that your account has been used without your consent, you should
  inform your security point-of-contact immediately.  When you do
  not know who your security point-of-contact is, try calling
  your Internet service provider's help desk as a first step.

6.1 How to Prepare for the Worst in Advance

   - Read all user documentation carefully.  Make sure that it is clear
     when services are being run on your computer.  If network services
     are activated, make sure they are properly configured (set all
     permissions so as to prevent anonymous or guest logins, and so
     on).  Increasingly, many programs have networking capabilities
     built in to them.  Learn how to properly configure and safely use
     these features.
   - Back up user data.  This is always important.  Backups are
     normally thought of as a way of ensuring you will not lose your
     work if a hard disk fails or if you make a mistake and delete a
     file.  Backing up is also critical to insure that data cannot be
     lost due to a computer security incident.  One of the most vicious
     and unfortunately common threats posed by computer viruses and
     Trojan Horse programs is erasing a computer's hard disk.
   - Obtain virus checking software or security auditing tools.  Learn
     how to use them and install them before connecting to a public
     network.  Many security tools require that they be run on a
     "clean" system, so that comparisons can be made between the
     present and pristine states.  Thus, it is necessary for some work
     to be done ahead of time.
   - Upgrade networking software regularly.  As new versions of
     programs come out, it is prudent to upgrade.  Security
     vulnerabilities will likely have been fixed.  The longer you wait
     to do this, the greater the risk that security vulnerabilities of
     the products will be become known and be exploited by some network
     assailant.  Keep up to date!
   - Find out who to contact if you suspect trouble.  Does your
     Internet Service Provider have a security contact or Help Desk?
     Investigate this before trouble happens so you won't lose time
     trying to figure it out should trouble occur.  Keep the contact
     information both online and offline for easy retrieval.

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  There are 3 ways to avoid problems with viruses:
     1. Don't be promiscuous
     If at all possible, be cautious about what software you install on
     your system. If you are unaware of or unsure of the origin of a
     program, it is wise not to run it.  Obtain software from trusted
     sources.  Do not execute programs or reboot using old diskettes
     unless you have reformatted them, especially if the old diskettes
     have been used to bring software home from a trade show and other
     potentially security-vulnerable places.
     Nearly all risk of getting infected by viruses can be eliminated
     if you are extremely cautious about what files are stored on your
     computer.  See "The Dangers of Downloading" for more details.
  2. Scan regularly.
     Give your system a regular check-up.  There are excellent
     virus checking and security audit tools for most computer
     platforms available today.  Use them, and if possible, set them to
     run automatically and regularly.  Also, install updates of these
     tools regularly and keep yourself informed of new virus threats.
  3. Notice the unusual.
     It's not true that a difference you cannot detect is no difference
     at all, but it is a good rule of thumb.  You should get used to
     the way your system works.  If there is an unexplainable change
     (for instance, files you believe should exist are gone, or strange
     new files are appearing and disk space is 'vanishing'), you should
     check for the presense of viruses.
  You should take some time to be familiar with computer virus
  detection tools available for your type of computer.  You should use
  an up-to-date tool (i.e. not older than three months).  It is very
  important to test your computer if you have been using shared
  software of dubious origin, someone else's used floppy disks to
  transfer files, and so on.

6.2 What To Do if You Suspect Trouble

  If you suspect that your home computer has a virus, that a malicious
  program has been run, or that a system has been broken into, the
  wisest course of action is to first disconnect the system from all
  networks.  If available, virus detection or system auditing software
  should be used.

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  Checking vital system files for corruption, tampering or malicious
  replacement is very tedious work to do by hand.  Fortunately there are
  many virus detection programs available for PCs and Macintosh
  computers.  There are security auditing programs available for
  UNIX-based computers.  If software is downloaded from the network, it
  is wise to run virus detection or auditing tools regularly.
  If it becomes clear that a home system has been attacked, it is time
  to clean up.  Ideally, a system should be rebuilt from scratch.  This
  means erasing everything on the hard disk.  Next, install the
  operating system and then all additional software the system needs.
  It is best to install the operating system and additional software
  from the original distribution diskettes or CD-roms, rather than from
  backup storage.  The reason for this is that a system may have been
  broken into some time ago, so the backed up system or program files
  may already include some altered files or viruses.  Restoring a system
  from scratch is tedious but worthwhile.  Do not forget to re-install
  all security related fixes you had installed before the security
  incident.  Obtain these from a verified, unsuspicious source.

6.3 Email

  Remember to be careful with saved Email.  Copies of sent or received
  Email (or indeed any file at all) placed in storage provided by an
  Internet service provider may be vulnerable.  The risk is that
  someone might break into the account and read the old Email.  Keep
  your Email files, indeed any sensitive files, on your home machine.

7. Home Alone

  A home system can be broken into over the Internet if a home user is
  unwary.  The files on the home system can be stolen, altered or
  destroyed.  The system itself, if compromised, could be accessed
  again some time in the future.  This section describes issues and
  makes recommendations relevant to a home user of the Internet.

7.1 Beware of Daemons

  A home system which uses PPP to connect directly to the Internet is
  increasingly common.  These systems are at the greatest risk if they
  run certain kinds of programs called "services".  If you run a
  service, you are in effect making your computer available to others
  across the network.  Some services include:
  - File servers (an NFS server, a PC with 'file sharing' turned on)
  - An FTP server
  - A Web server

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  There are, in general, two types of programs which operate on the
  Internet:  Clients (like web browsers and Email programs) and Servers
  (like web servers and mail servers).
  Most software which runs on home systems is of the client variety;
  but, increasingly, server software is available on traditionally
  client platforms (e.g., PCs).  Server software which runs in the
  background is referred to as a "daemon" (pronounced dee-mon).  Many
  Internet server software programs that run as daemons have names that
  end in `d', like "inetd" (Internet Daemon) and "talkd" (Talk Daemon).
  When set to run, these programs wait for clients to request some
  particular service from across the network.
  There are four very important things to keep in mind as far as the
  security implications of running services on a home computer are
   - First and most important, if a server is not properly configured,
     it is very vulnerable to being attacked over a network.  It is
     vital, if you run services, to be familiar with the proper
     configuration.  This is often not easy, and may require training
     or technical expertise.
   - All software has flaws, and flaws exploited deviously can be used
     to breach computer security.  If you run a server on your home
     machine, you have to stay aware.  This requires work:  You have to
     stay in touch with the supplier of the software to get security
     updates.  It is highly recommended that you keep up with security
     issues through on-line security forums. See [RFC2196] for a list
     of references.
     If security flaws in your server software are discovered, you will
     need to either stop using the software or apply "patches" or
     "fixes" which eliminate the vulnerability.  The supplier of the
     software, if it is a decent company or freeware author, will
     supply information and updates to correct security flaws.  These
     "patches" or "fixes" must be installed as soon as possible.
   - As a rule of thumb, the older the software, the greater the chance
     that it has known vulnerabilities. This is not to say you should
     simply trust brand new software either!  Often, it takes time to
     discover even obvious security flaws in servers.
   - Some servers start up without any warning.  There are some web
     browsers and telnet clients which automatically start FTP servers
     if not explicitly configured to not do so.  If these servers are
     not themselves properly configured, the entire file system of the
     home computer can become available to anyone on the Internet.

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  In general, any software MAY start up a network daemon.  The way to
  be safe here is to know the products you are using.  Read the manual,
  and if any questions arise, call the company or mail the author of
  free software to find out if you are actually running a service by
  using the product.
  A home user running a remote login service on his home machine faces
  very serious risks.  This service allows the home user to log in to
  his home machine from other computers on the Internet and can be
  quite convenient.  But the danger is that someone will secretly
  observe the logging in and then be able to masquerade as the user
  whenever they choose to do so in the future.  See "The Wires Have
  Ears" which suggests precautions to take for remote log in.
  If possible, activate all "logging" options in your server software
  which relate to security.  You need to review these logs regularly in
  order to gain any benefit from this logging.  You should also be
  aware that logs often grow very quickly in size, so you need to be
  careful they don't fill up your hard disk!

7.2 Going Places

  Remote logins allow a user privileged access onto physically remote
  systems from the comfort of his own home.
  More and more companies are offering their employees the ability to
  work from home with access to their computer accounts through dial-up
  connections.  As the convenience of Internet connectivity has led to
  lowered costs and wide-spread availability, companies may allow
  remote login to their systems via the Internet.  Customers of
  companies with Internet access may also be provided with remote login
  accounts.  These companies include Internet service providers, and
  even banks.  Users should be very careful when making remote logins.
  As discussed in "The Wires have Ears" section, Internet connections
  can be eavesdropped on.  If you intend to use a remote login service,
  check that the connection can be done securely, and make sure that
  you use the secure technologies/features.
  Connections may be secured using technologies like one-time
  passwords, secure shell (SSH) and Secure Sockets Layer (SSL).  One-
  time passwords make a stolen password useless to steal, while secure
  shell encrypts data sent over the connection.  Please refer to "Don't
  Get Caught in the Web" for a discussion on SSL.  Secure services such
  as these have to be made available on the systems to which you log in

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7.3 Secure It!

  Administering your own home computer means you get to choose what
  software is run on it.  Encryption software provides protection for
  data.  If you keep business records and other sensitive data on your
  computer, encryption will help to keep it safe.  For example, if you
  ran a network service from your home computer and missed setting
  restrictions on a private directory, a remote user (authorized or
  not) may gain access to files in this private directory.  If the
  files are encrypted, the user will not be able to read them.  But as
  with all forms of encryption running on any system, the keys and
  passwords should first be kept safe!

8. A Final Note

  This document has provided the reader with an introduction and as
  much concise detail as possible.  Present security issues go out of
  date quickly, and although effort has been made to keep discussions
  general, examples given may not be relevant in the future as the
  Internet and computer industry continue to grow.
  Just as home-owners are now taking increased cautions at the expense
  of convenience, to secure their homes in the changing world we live
  in, computer network users should not ignore security.  It may be
  inconvenient, but it is always better to be safe than sorry.

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Appendix: Glossary of Security Terms

  Acceptable Use Policy (AUP)
     A set of rules and guidelines that specify in more or less detail
     the expectations in regard to appropriate use of systems or
     See (Computer) Account
  Anonymous and Guest Log In
     Services may be made available without any kind of authentication.
     This is commonly done, for instance, with the FTP protocol to
     allow anonymous access.  Other systems provide a special account
     named "guest" to provide access, typically restricting the
     privileges of this account.
  Auditing Tool
     Tools to analyze computer systems or networks in regard to their
     security status or in relation to the set of services provided by
     them.  COPS (Computer Oracle Password and Security analyzer) and
     SATAN (Security Administrator's Tool for Analyzing Networks) are
     famous examples of such tools.
     Authentication refers to mechanisms which are used to verify the
     identity of a user.  The process of authentication typically
     requires a name and a password to be supplied by the user as proof
     of his identity.
  Centrally-Administered Network
     A network of systems which is the responsibility of a single group
     of administrators who are not distributed but work centrally to
     take care of the network.
     Certificates are data which is used to verify digital signatures.
     A certificate is only as trustworthy as the agency which issued
     it.  A certificate is used to verify a particular signed item,
     such as an Email message or a web page.  The digital signature,
     the item and the certificate are all processed by a mathematical

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     program. It is possible to say, if the signature is valid, that
     "According to the agency which issued the certificate, the signer
     was (some name)".
  Clean System
     A computer which has been freshly installed with its operating
     system and software obtainied from trusted software distribution
     media.  As more software and configuration are added to a
     computer, it becomes increasingly difficult to determine if the
     computer is 'clean' or has been compromised by viruses, trojan
     horse or misconfiguration which reduces the security of the
     Depending on the point of view, a client might be a computer
     system which an end-user uses to access services hosted on another
     computer system called a server.  'Client' may also refer to a
     program or a part of a system that is used by an end-user to
     access services provided by another program (for example, a web
     browser is a client that accesses pages provided by a Web Server).
  Compound Documents
     A 'document' is a file containing (a set of) data.  Files may
     consist of multiple parts: a plain document, an encrypted
     document, a digitally-signed documents or a compressed document.
     Multi-part files are known as compound documents and may require a
     variety of programs to be used in order to interpret and
     manipulate it.  These programs may be used without the user's
  (Computer) Account
     This term describes the authorization to access a specific
     computer system or network.  Each end-user has to use an account,
     which consists most probably of a combination of user name and
     password or another means of proving that the end-user is the
     person the account is assigned to.
  Configuring Network Services
     The part of an administrator's task that is related to specifying
     the conditions and details of network services that govern the
     service provision.  In regard to a Web server, this includes which
     Web pages are available to whom and what kind of information is
     logged for later review purposes.

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     Cookies register information about a visit to a web site for
     future use by the server.  A server may receive information of
     cookies of other sites as well which create concern in terms of
     breach of privacy.
     This term is used to describe attackers, intruders or other bad
     guys that do not play by the rules and try to circumvent security
     mechanisms and/or attack individuals and organisations.
  Daemons (inetd, talkd, etc.)
     These are processes that run on computer systems to provide
     services to other computer systems or processes.  Typically,
     daemons are considered "servers".
     The process of reversing the encryption of a file or message to
     recover the original data in order to use or read it.
  Default Account
     Some systems and server software come with preconfigured accounts.
     These accounts may be set up with a predefined (user name and)
     password to allow anyone access and are often put there to make it
     convenient for users to login initially.  Default accounts should
     be turned off or have their predefined passwords changed, to
     reduce the risk of abuse to the system.
  Dial-in Service
     A way of providing access to computer systems or networks via a
     telecommunications network.  A computer uses a modem to make a
     telephone call to a another modem, which in turn provides 'network
     access service'.  See also: PPP.
  Digital Signature
     A digital signature is created by a mathematical computer program.
     It is not a hand-written signature nor a computer-produced picture
     of one.  The signature is like a wax seal that requires a special
     stamp to produce it, and is attached to an Email message or file.
     The origin of the message or file may then be verified by the
     digital signature (using special tools).

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  Downloaded Software
     Software packages retrieved from the Internet (using, for example,
     the FTP protocol).
     The act of retrieving files from a server on the network.
  Email Packages
     To communicate via electronic mail, an end-user usually makes use
     of an Email client that provides the user-interface to create,
     send, retrieve and read Email. Various different Email packages
     provide the same set of basic functions but have different user-
     interfaces and perhaps, special/extra functions.  Some Email
     packages provide encryption and digital signature capabilities.
  Email Security Software
     Software which provides security through digital signatures and
     encryption (and decryption) to enable the end-user to protect
     messages and documents prior to sending them over a possibly
     insecure network.  PGP is an example of such software.
  Encrypting / Encryption
     This is a mathematical process of scambling data for privacy
  Encryption Software
     The software that actually provides the needed functionality for
     end users to encrypt messages and files. PGP is one example.
     An (human) individual that makes use of computer systems and
  Files (programs, data, text and so on)
     Files include user data, but also programs, the computer operating
     system and the system's configuration data.

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  File Server
     A computer system that provides a way of sharing and working on
     files stored on the system among users with access to these files
     over a network.
  File Transfer
     The process of transferring files between two computer systems
     over a network, using a protocol such as FTP or HTTP.
  Fixes, Patches and installing them
     Vendors, in response to the discovery of security vulnerabilities,
     provide sets of files that have to be installed on computer
     systems.  These files 'fix' or 'patch' the computer system or
     programs and remove the security vulnerability.
  FTP (File Transfer Protocol)
     A protocol that allows for the transfer of files between an FTP
     client and FTP server.
  Group of Users
     Security software often allow permissions to be set for groups (of
     users) as opposed to individuals.
  Help Desk
     A support entity that can be called upon to get help with a
     computer or communication problem.
     A collection of interconnected networks that use a common set of
     protocols called the TCP/IP stack to enable communication between
     the connected computer systems.
  Key Escrow
     Keys are used to encrypt and decrypt files.  key escrow is used to
     store keys for use by third parties to access the data in
     encrypted files.

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  Keys Used to Encrypt and Decrypt Files
     To make use of encryption, an end-user has to provide some secret,
     in the form of some data, usually called a key.
  Log In, Logging into a System
     This is an action performed by an end-user, when he authenticates
     himself to a computer system.
  Log In Prompt
     The characters that are displayed when logging into a system to
     ask for user name and password.
  Logged In
     If an end-user has successfully proven to have legitimate access
     to a system, he is considered to be logged in.
     Systems and server software often provide the ability to keep
     track of events.  Events may be configured to be written out to a
     file known as a log.  The log file can be read later and allows
     for system failures and security breaches to be identified.
  Masquerade (see Remote Log In)
     Anyone who pretends to be someone they are not in order to obtain
     access to a computer account is said to be in 'masquerade'.  This
     may be accomplished by providing a false user name, or stealing
     someone else's password and logging in as him.
  Network File System (NFS, file sharing with PCs, etc.)
     NFS is an application and protocol suite that provides a way of
     sharing files between clients and servers. There are other
     protocols which provide file access over networks.  These provide
     similar functionality, but do not interoperate with each other.
  Networking Features of Software
     Some software has features which make use of the network to
     retrieve or share data.  It may not be obvious that software has
     networking features.

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  Network Services
     Services which are not provided on the local computer system the
     end-user is working on but on a server located in the network.
  One-Time Passwords (OTP)
     Instead of using the same password over and over again, a
     different password is used on each subsequent log in.
     A passphrase is a long password.  It is often composed of several
     words and symbols to make it harder to guess.
  Password-Locked Screensaver
     A screen saver obscures the normal display of a monitor.  A
     password-locked screensaver can only be deactivated if the end-
     user's password is supplied.  This prevents a logged-in system
     from being abused and hides the work currently being done from
     See "Fixes, Patches and installing them"
     Another word for the access controls that are used to control the
     access to files and other resources.
  PGP (Pretty Good Privacy)
     PGP is an application package that provides tools to encrypt and
     digitally sign files on computer systems.  It is especially useful
     to encrypt and/or sign files and messages before sending them via
  Plug-in Modules
     Software components that integrate into other software (such as
     web browsers) to provide additional features.

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  Point-of-Contact, Security
     In case of security breaches or problems, many organisations
     provide a designated point-of-contact which can alert others and
     take the appropriate actions.
  PPP (Point to Point Protocol)
     PPP is the mechanism which most end-users establish a network
     connection between their PC and their Internet service provider
     with.  Once connected, the PC is able to transmit and receive data
     to any other system on the network.
  Privacy Programs
     Another term for encryption software that highlights the use of
     this software to protect the confidentiality and therefore privacy
     of the end-users that make use of it.
  Remote Access Software
     This software allows a computer to use a modem to connect to
     another system.  It also allows a computer to 'listen' for calls
     on a modem (this computer provides 'remote access service'.)
     Remote access software may provide access to a single computer or
     to a network.
  Remote Log In
     If an end-user uses a network to log in to a system, this act is
     known as remote log in.
  Security Features
     These are features which provide protection or enable end-users
     and administrators to assess the security of a system, for
     example, by auditing it.
  Security Policy
     A security policy is written by organisations to address security
     issues, in the form of "do's" and "don'ts".  These guidelines and
     rules are for users with respect to physical security, data
     security, information security and content (eg. rules stating that
     sites with sexual content should not be visited, and that
     copyrights should be honoured when downloading software, etc).

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     A server is a computer system, or a set of processes on a computer
     system providing services to clients across a network.
  Shared Account
     A common account is one which is shared by a group of users as
     opposed to a normal account which is available to only one user.
     If the account is misused, it is very difficult or impossible to
     know which of users was responsible.
  Sharing Permissions
     Many computer systems allow users to share files over a network.
     These systems invariably provide a mechanism for users to use to
     control who has permission to read or overwrite these files.
     Depending on the context in which this term is used, it might
     apply to computer systems that are grouped together by
     geographical location, organizational jurisdiction, or network
     addresses.  A Site typically refers to a network under a common
  SSH (Secure Shell)
     SSH provides a protocol between a client and server, allowing for
     encrypted remote connectivity.
  SSL (Secure Sockets Layer)
     This protocol provides security services to otherwise insecure
     protocols which operate over a network.  SSL is typically used by
     web browsers to encrypt data sent to and downloaded from a server.
  Systems Administrator
     The individual who maintains the system and has system
     administrator privileges. In order to avoid errors and mistakes
     done by this individual while not acting as an administrator,
     he/she should limit the time he/she acts as an administrator (as
     known to the system) to a minimum.

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RFC 2504 Users' Security Handbook February 1999

  System Administrator Privileges
     System administrators have more rights (greater permissions) as
     their work involve the maintenance of system files.
  System Files
     The set of files on a system that do not belong to end-users,
     which govern the functionality of the system.   System files have
     a great impact on the security of the system.
     A protocol that enables remote log in to other computer systems
     over the network.
     A dumb device that is connected to a computer system in order to
     provide (text-based) access to it for users and administrators.
  Terms of Service (TOS)
     See "Acceptable Use Policy (AUP)".
     The potential that an existing vulnerability can be exploited to
     compromise the security of systems or networks. Even if a
     vulnerability is not known, it represents a threat by this
  Trojan Horse
     A program which carries within itself a means to allow the creator
     of the program access to the system using it.
     A program which replicates itself on computer systems by
     incorporating itself (secretly and maliciously) into other
     programs.  A virus can be transferred onto a computer system in a
     variety of ways.
  Virus-Detection Tool
     Software that detects and possibly removes computer viruses,
     alerting the user appropriately.

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RFC 2504 Users' Security Handbook February 1999

     A vulnerability is the existence of a weakness, design, or
     implementation error that can lead to an unexpected, undesirable
     event compromising the security of the system, network,
     application, or protocol involved.
  Web Browser Cache
     This is the part of the file system that is used to store web
     pages and related files.  It can be utilized to reload recently
     accessed files from the cache instead of loading it every time
     from the network.
  Web Browser Capabilities
     The set of functionalities on a web browser for use by the end-
     user.  This includes the set of plug-ins available.
  Web Server
     A server program that provides access to web pages.  Some web
     servers provide access to other services, such as databases, and
     A computer program which replicates itself and is self-
     propogating.  Worms, as opposed to viruses, are meant to spawn in
     network environments.


  The User Security Handbook was a collaborative effort of the Site
  Security Handbook Working Group of the IETF.  There were also others
  who made significant contributions --- Simson Garfinkle and Eric
  Luiijf provided very helpful feedback on this document.  The Glossary
  contribution by Klaus-Peter Kossakowski is much appreciated.


  [GLOSSARY] Malkin, G., Ed., "Internet User's Glossary", FYI 18, RFC
             1983 August 1996.
  [RFC2196]  Fraser, B., Ed., "Site Security Handbook", FYI 8, RFC 2196
             September 1997.

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RFC 2504 Users' Security Handbook February 1999

Security Considerations

  This document discusses what computer users can do to improve
  security on their systems.

Authors' Addresses

  Erik Guttman
  Sun Microsystems
  Bahnstr. 2
  74915 Waibstadt
  Phone: +49 7263 911701

  Lorna Leong
  COLT Internet
  250 City Road
  City Forum, London
  Phone: +44 171 390 3900

  Gary Malkin
  Bay Networks
  8 Federal Street
  Billerca, MA 01821
  Phone: +1 508 916 4237

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RFC 2504 Users' Security Handbook February 1999

Full Copyright Statement

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