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@DDDDDDDDDDD6 Computer Viruses & Threats II GDDDDDDDDDDDY
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$_Virus Prevention in General
To provide general protection from attacks by computer viruses,
unauthorized users, and related threats, users and managers need
to eliminate or reduce vulnerabilities. A general summary of the
vulnerabilities that computer viruses and related threats are
most likely to exploit is as follows:
- lack of user awareness - users copy and share infected
software, fail to detect signs of virus activity, do not
understand proper security techniques
- absence of or inadequate security controls - personal
computers generally lack software and hardware security
mechanisms that help to prevent and detect unauthorized
use, existing controls on multi-user systems can
sometimes be surmounted by knowledgeable users
- ineffective use of existing security controls - using
easily guessed passwords, failing to use access controls,
granting users more access to resources than necessary
- bugs and loopholes in system software - enabling
knowledgeable users to break into systems or exceed their
authorized privileges
- unauthorized use - unauthorized users can break in to
systems, authorized users can exceed levels of privilege
and misuse systems
- susceptibility of networks to misuse - networks can
provide anonymous access to systems, many are in general
only as secure as the systems which use them
As can be seen from this summary, virus prevention requires that
many diverse vulnerabilities be addressed. Some of the
vulnerabilities can be improved upon significantly, such as
security controls that can be added or improved, while others are
somewhat inherent in computing, such as the risk that users will
not use security controls or follow policies, or the risk of
unauthorized use of computers and networks. Thus, it may not be
possible to completely protect systems from all virus-like
attacks. However, to attain a realistic degree of protection,
all areas of vulnerability must be addressed; improving upon some
areas at the expense of others will still leave significant holes
in security.
To adequately address all areas of vulnerability, the active
involvement of individual users, the management structure, and
the organization in a virus prevention program is essential.
Such a program, whether formal or informal, depends on the mutual
cooperation of the three groups to identify vulnerabilities, to
take steps to correct them, and to monitor the results.
A virus prevention program must be initially based upon effective
system computer administration that restricts access to
authorized users, ensures that hardware and software are
regularly monitored and maintained, makes backups regularly, and
maintains contingency procedures for potential problems. Sites
that do not maintain a basic computer administration program need
to put one into place, regardless of their size or the types of
computers used. Many system vendors supply system administration
manuals that describe the aspects of a basic program.
Once a basic administration program is in place, management and
users need to incorporate virus prevention measures that will
help to deter attacks by viruses and related threats, detect when
they occur, contain the attacks to limit damage, and recover in a
reasonable amount of time without loss of data. To accomplish
these aims, attention needs to be focused on the following areas:
- educating users about malicious software in general, the
risks that it poses, how to use control measures,
policies, and procedures to protect themselves and the
organization
- software management policies and procedures that address
public-domain software, and the use and maintenance of
software in general
- use of technical controls that help to prevent and deter
attacks by malicious software and unauthorized users
- monitoring of user and software activity to detect signs
of attacks, to detect policy violations, and to monitor
the overall effectiveness of policies, procedures, and
controls
- contingency policies and procedures for containing and
recovering from attacks
General guidance in each of these areas is explained in the
following sections.
$_Education
Education is one of the primary methods by which systems and
organizations can achieve greater protection from incidents of
malicious software and unauthorized use. In situations where
technical controls do not provide complete protection (i.e., most
computers), it is ultimately people and their willingness to
adhere to security policies that will determine whether systems
and organizations are protected. By educating users about the
general nature of computer viruses and related threats, an
organization can improve its ability to deter, detect, contain
Users should be educated about the following:
- how malicious software operates, methods by which it is
planted and spread, the vulnerabilities exploited by
malicious software and unauthorized users
- general security policies and procedures and how to use
them
- the policies to follow regarding the backup, storage, and
use of software, especially public-domain software and
shareware
- how to use the technical controls they have at their
disposal to protect themselves
- how to monitor their systems and software to detect signs
of abnormal activity, what to do or whom to contact for
more information
- contingency procedures for containing and recovering from
potential incidents
User education, while perhaps expensive in terms of time and
resources required, is ultimately a cost-effective measure for
protecting against incidents of malicious software and
unauthorized use. Users who are better acquainted with the
destructive potential of malicious software and the methods by
which it can attack systems may in turn be prompted to take
measures to protect themselves. The purpose of security policies
and procedures will be more clear, thus users may be more willing
to actively use them. By educating users how to detect abnormal
system activity and the resultant steps to follow for containing
and recovering from potential incidents, organizations will save
money and time if and when actual incidents occur.
$_Software Management
As shown by examples in File 1, one of the prime methods by
which malicious software is initially copied onto systems is by
unsuspecting users. When users download programs from sources
such as software bulletin boards, or public directories on
systems or network servers, or in general use and share software
that has not been obtained from a reputable source, users are in
danger of spreading malicious software. To prevent users from
potentially spreading malicious software, managers need to
- ensure that users understand the nature of malicious
software, how it is generally spread, and the technical
controls to use to protect themselves
- develop policies for the downloading and use of public-
domain and shareware software
- create some mechanism for validating such software prior
to allowing users to copy and use it
- minimize the exchange of executable software within an
organization as much as possible
- do not create software repositories on LAN servers or in
multi-user system directories unless technical controls
exist to prevent users from freely uploading or
downloading the software
The role of education is important, as users who do not
understand the risks yet who are asked to follow necessarily
restrictive policies may share and copy software anyway. Where
technical controls cannot prevent placing new software onto a
system, users are then primarily responsible for the success or
failure of whatever policies are developed.
A policy that prohibits any copying or use of public-domain
software may be overly restrictive, as some public domain
programs have proved to be useful. A less restrictive policy
would allow some copying, however a user might first require
permission from the appropriate manager. A special system should
be used from which to perform the copy and then to test the
software. This type of system, called an isolated system, should
be configured so that there is no risk of spreading a potentially
malicious program to other areas of an organization. The system
should not be used by other users, should not connect to
networks, and should not contain any valuable data. An isolated
system should also be used to test internally developed software
and updates to vendor software.
Other policies for managing vendor software should be developed.
These policies should control how and where software is
purchased, and should govern where the software is installed and
how it is to be used. The following policies and procedures are
suggested:
- purchase vendor software only from reputable sources
- maintain the software properly and update it as necessary
- don't use pirated software, as it may have been modified
- keep records of where software is installed readily
available for contingency purposes
- ensure that vendors can be contacted quickly if problems
occur
- store the original disks or tapes from the vendor in a
secure location
$_Technical Controls
Technical controls are the mechanisms used to protect the
security and integrity of systems and associated data. The use
of technical controls can help to prevent occurrences of viruses
and related threats by deterring them or making it more difficult
for them to gain access to systems and data. Examples of
technical controls include user authentication mechanisms such as
passwords, mechanisms which provide selective levels of access to
files and directories (read-only, no access, access to certain
users, etc.), and write-protection mechanisms on tapes and
diskettes.
The different types of technical controls and the degree to which
they can provide protection and deterrence varies from system to
system, thus the use of specific types of controls is discussed
in the following files. However, the following general points are
important to note:
- technical controls should be used as available to
restrict system access to authorized users only
- in the multi-user environment, technical controls should
be used to limit users' privileges to the minimum
practical level; they should work automatically and need
not be initiated by users
- users and system managers must be educated as to how and
when to use technical controls
- where technical controls are weak or non-existent (i.e.,
personal computers), they should be supplemented with
alternative physical controls or add-on control
mechanisms
Managers need to determine which technical controls are available
on their systems, and then the degree to which they should be
used and whether additional add-on controls are necessary. One
way to answer these questions is to first categorize the
different classes of data being processed by a system or systems,
and then to rank the categories according to criteria such as
sensitivity to the organization and vulnerability of the system
to attack. The rankings should then help determine the degree to
which the controls should be applied and whether additional
controls are necessary. Ideally, those systems with the most
effective controls should be used to process the most sensitive
data, and vice-versa. As an example, a personal computer which
processes sensitive employee information should require add-on
user authentication mechanisms, whereas a personal computer used
for general word processing may not need additional controls.
It is important to note that technical controls do not generally
provide complete protection against viruses and related threats.
They may be cracked by determined users who are knowledgeable of
hidden bugs and weaknesses, and they may be surmounted through
the use of Trojan horse programs, as shown by examples in File
1. An inherent weakness in technical controls is that, while
deterring users and software from objects to which they do not
have access, they may be totally ineffective against attacks
which target objects that are accessible. For example, technical
controls may not prevent an authorized user from destroying files
to which the user has authorized access. Most importantly, when
technical controls are not used properly, they may increase a
system's degree of vulnerability. It is generally agreed that
fully effective technical controls will not be widely available
for some time. Because of the immediate nature of the computer
virus threat, technical controls must be supplemented by less
technically-oriented control measures such as described in this
chapter.
$_General Monitoring
An important aspect of computer viruses and related threats is
that they potentially can cause extensive damage within a very
small amount of time, such as minutes or seconds. Through proper
monitoring of software, system activity, and in some cases user
activity, managers can increase their chances that they will
detect early signs of malicious software and unauthorized
activity. Once the presence is noted or suspected, managers can
then use contingency procedures to contain the activity and
recover from whatever damage has been caused. An additional
benefit of general monitoring is that over time, it can aid in
determining the necessary level or degree of security by
indicating whether security policies, procedures, and controls
are working as planned.
Monitoring is a combination of continual system and system
management activity. Its effectiveness depends on cooperation
between management and users. The following items are necessary
for effective monitoring:
- user education - users must know, specific to their
computing environment, what constitutes normal and
abnormal system activity and whom to contact for further
information - this is especially important for users of
personal computers, which generally lack automated
methods for monitoring
- automated system monitoring tools - generally on multi-
user systems, to automate logging or accounting of user
and software accesses to accounts, files, and other
system objects - can sometimes be tuned to record only
certain types of accesses such as "illegal" accesses
- anti-viral software - generally on personal computers,
these tools alert users of certain types of system access
that are indicative of "typical" malicious software
- system-sweep programs - programs to automatically check
files for changes in size, date, or content
- network monitoring tools - as with system monitoring
tools, to record network accesses or attempts to access
The statistics gained from monitoring activities should be used
as input for periodic reviews of security programs. The reviews
should evaluate the effectiveness of general system management,
and associated security policies, procedures, and controls. The
statistics will indicate the need for changes and will help to
fine tune the program so that security is distributed to where it
is most necessary. The reviews should also incorporate users'
suggestions, and to ensure that the program is not overly
restrictive, their criticisms.
$_Contingency Planning
The purpose of contingency planning with regard to computer
viruses and related threats is to be able to contain and recover
completely from actual attacks. In many ways, effective system
management that includes user education, use of technical
controls, software management, and monitoring activities, is a
form of contingency planning, generally because a well-run,
organized system or facility is better able to withstand the
disruption that could result from a computer virus attack. In
addition to effective system management activities, managers need
to consider other contingency procedures that specifically take
into account the nature of computer viruses and related threats.
Possibly the most important contingency planning activity
involves the use of backups. The ability to recover from a virus
attack depends upon maintaining regular, frequent backups of all
system data. Each backup should be checked to ensure that the
backup media has not been corrupted. Backup media could easily
be corrupted because of defects, because the backup procedure was
incorrect, or perhaps because the backup software itself has been
attacked and modified to corrupt backups as they are made.
Contingency procedures for restoring from backups after a virus
attack are equally important. Backups may contain copies of
malicious software that have been hiding in the system.
Restoring the malicious software to a system that has been
attacked could cause a recurrence of the problem. To avoid this
possibility, software should be restored only from its original
media: the tapes or diskettes from the vendor. In some cases,
this may involve reconfiguring the software, therefore managers
must maintain copies of configuration information for system and
application software. Because data is not directly executable,
it can be restored from routine backups. However, data that has
been damaged may need to be restored manually or from older
backups. Command files such as batch procedures and files
executed when systems boot or when user log on should be
inspected to ensure that they have not been damaged or modified.
Thus, managers will need to retain successive versions of
backups, and search through them when restoring damaged data and
command files.
Other contingency procedures for containing virus attacks need to
be developed. The following are suggested; they are discussed in
more detail in following files:
- ensure that accurate records are kept of each system's
configuration, including the system's location, the
software it runs, the system's network and modem
connections, and the name of the system's manager or
responsible individual
- create a group of skilled users to deal with virus
incidents and ensure that users can quickly contact this
group if they suspect signs of viral activity
- maintain a security distribution list at each site with
appropriate telephone numbers of managers to contact when
problems occur
- isolate critical systems from networks and other sources
of infection
- place outside network connections on systems with the
best protections, use central gateways to facilitate
rapid disconnects
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