Chapter 29 Anti-Virus

29.7 Anti-Virus Technical Reference

Types of Computer Viruses

The following table describes some of the common computer viruses.

Table 141 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

This type of virus infects the area of a hard drive that a computer

Virus

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

A polymorphic virus (also known as a mutation virus) tries to evade

Virus

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.

 

 

Computer Virus Infection and Prevention

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

1A 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.

2The virus spreads to other files and programs on the computer.

3The infected files are unintentionally sent to another computer thus starting the spread of the virus.

4Once the virus is spread through the network, the number of infected networked computers can grow exponentially.

Types of Anti-Virus Scanner

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

 

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