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Chapter 28 Anti-Virus
ZyWALL USG 100/200 Series User’s Guide
480
28.7 Anti-Virus Technical Reference
Types of Computer Viruses
The following table describes some of the common computer viruses.
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.
2 The virus spreads to other files and programs on the computer.
3 The infected files are unintentionally sent to another computer thus starting the spread of
the virus.
4 Once 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.
A host-based anti-virus (HAV) scanner is often software installed on computers and/or servers
in the network. It inspects files for virus patterns as they are moved in and out of the hard
drive. However, host-based anti-virus scanners cannot eliminate all viruses for a number of
reasons:
Severity This is the severity level of the anti-virus signature. Click the severity column
header to sort your search results by ascending or descending severity.
Category This column displays whether the signature is for identifying a virus or spyware.
Click the column heading to sort your search results by category.
Table 150 Anti-X > Anti-Virus > Signature (continued)
LABEL DESCRIPTION
Table 151 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.
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.