ZyXEL Communications 70 Series User Manual

ZyWALL 5/35/70 Series User’s Guide

Chapter 14 Anti-Virus

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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. 

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. 

Table 82   Common Computer Virus Types 

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.