ZyXEL Communications 1000 Manual De Usuario

 Chapter 33 Anti-Virus

ZyWALL USG 1000 User’s Guide

The following table describes some of the common computer viruses. 

The following describes a simple life cycle of a computer virus. 

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. 

The virus spreads to other files and programs on the computer. 

The infected files are unintentionally sent to another computer thus starting the 
spread of the virus. 

Once the virus is spread through the network, the number of infected networked 
computers can grow exponentially.  

The section describes two types of anti-virus scanner: host-based and network-
based. 

Table 149   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.  

Polymorphic 
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.