ZyXEL Communications Internet Security Appliance ZyWALL5UTM 4.0 - Manual (Page 254)

ZyWALL 5/35/70 Series User’s Guide
Chapter 14 Anti-Virus 254
C
H A P T E R
14
Anti-Virus
This chapter introduces and shows you how to configure the anti-virus scanner.
14.1 Anti-Virus Overview
A computer virus is a small program designed to corrupt and/or alter the operation of other
legitimate programs. A worm is a self-replicating virus that resides in active memory and
duplicates itself. The effect of a virus attack varies from doing so little damage that you are
unaware your computer is infected to wiping out the entire contents of a hard drive to
rendering your computer inoperable.
14.1.1 Types of Computer Viruses
The following table describes some of the common computer viruses.
Table 82 Common Computer Virus Types
TYPE DESCRIPTION
File Infector This is a small program that embeds itself in a legitimate program. A file infector is
able to copy and attach itself to other programs that are executed on an infected
computer.
Boot Sector Virus This type of virus infects the area of a hard drive that a computer reads and
executes during startup. The virus causes computer crashes and to some extend
renders the infected computer inoperable.
Macro Virus Macro viruses or Macros are small programs that are created to perform repetitive
actions. Macros run automatically when a file to which they are attached is
opened. Macros spread more rapidly than other types of viruses as data files are
often shared on a network.
E-mail Virus E-mail viruses are malicious programs that spread through e-mail.
Polyphormic Virus A polymorphic virus (also known as a mutation virus) tries to evade detection by
changing a portion of its code structure after each execution or self replication.
This makes it harder for an anti-virus scanner to detect or intercept it.
A polymorphic virus can also belong to any of the virus types discussed above.
14.1.2 Computer Virus Infection and Prevention
The following describes a simple life cycle of a computer virus.
1 A computer gets a copy of a virus from a source such as the Internet, e-mail, file sharing
or any removable storage media. The virus is harmless until the execution of an infected
program.