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Introduction
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In order to be aware of potential threats to your computer, it is helpful to know
what the types of malicious software (“malware”) are and how they work. In
general, malicious programs fall into one of the following three categories:
•
Worms use network protection vulnerabilities for distribution. These pro-
grams were called "worms" because of their ability to tunnel from one
computer to another, using networks, email and other channels. Due to
this ability, worms can spread extremely fast.
Worms penetrate a computer, determine IP addresses of other
computers, and send copies of themselves to these computers. Worms
also utilize data contained in the address books of mail clients installed on
the infected machine for sending infected messages. They can create
work files on disks but may not utilize any resources of the infected
computer except memory.
Penetration of a worm is a preliminary stage that is often followed by
penetration of other malicious programs into the infected computer. For
example, a worm may identify some vulnerabilities that Trojans will use
later to penetrate the computer.
•
Viruses infect computer programs by altering the way that infected pro-
grams work to gain control over the infected files when such files are run.
This simple definition helps determine that the main action a virus per-
forms is infecting computer programs. Viruses spread somewhat slower
than worms.
•
Trojan horses perform unauthorized actions on infected computers: for
instance, they can erase information on hard drives, "freeze" the system,
steal confidential information. In the strict sense, Trojan Horses are not vi-
ruses as they do not infect programs or data, and are unable to sneak in-
dependently into computers but are distributed by malicious users as
"useful" software. Still the damage inflicted by Trojans may be far greater
than from a regular virus attack.
Recently, worms have become the most widespread type of malware, followed
by viruses and Trojans. Some malicious computer programs have characteristics
of two or even all three of the above categories.
The following potentially dangerous types of malware have also become
widespread:
Adware – code that, without the user's knowledge, is included into a program's
code in order to display advertising messages. As a rule, adware is
integrated into freeware programs. The advertising component is located in
the interface. Adware programs are often used to gather users' personal
information and send it to the developer, change browser's settings
(browser's home page, search page, security levels, etc.) and create traffic
that is not controlled by the user. All this may lead to the infringement of the
security policy and further to direct financial losses.