Chapter 14 Anti-Virus; Anti-Virus Overview; Types Of Computer Viruses; Computer Virus Infection And Prevention - ZyXEL Communications 35 Series User Manual

Internet security appliance

Table of Contents

This chapter introduces and shows you how to configure the anti-virus scanner.

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.

The following table describes some of the common computer viruses.

File Infector

Boot Sector Virus

E-mail Virus

Polyphormic Virus

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

Chapter 14 Anti-Virus

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

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 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 viruses are malicious programs that spread through e-mail.

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.

ZyWALL 5/35/70 Series User's Guide

Table of Contents