System information

Threats to computer security 17
MALICIOUS PROGRAMS
Malicious programs are created specifically to inflict harm to computers and
their users: steal, block, modify or erase information, disrupt the operation of
computers or computer networks.
Malware programs are divided into three subcategories: viruses and worms,
Trojans programs and malware utilities.
Viruses and worms (see page 17) (Viruses_and_Worms) can create copies of
themselves which are, in turn, capable of creating their own copies. Some of
them run without user's knowledge or participation, others require actions on the
user's part to be run. These programs perform their malicious actions when run.
Trojan programs (see page 20) (Trojan_programs) do not create copies of
themselves, unlike worms and viruses. They sneak into a computer, for example,
via e-mail or using a web browser when the user visits an "infected" website. To
be launched they require user's actions and start performing their malicious
actions as they run.
Malware utilities (see page 26) (Malicious_tools) are created specifically to inflict
damage. However, unlike other malware programs, they do not perform
malicious actions immediately as they are run and can be safely stored and run
on the user's computer. Such programs have functions used to create viruses,
worms and Trojan programs, arrange network attacks on remote servers,
hacking computers or other malicious actions.
VIRUSES AND WORMS
Subcategory: viruses and worms (Viruses_and_Worms)
Severity level: high
Classic viruses and worms perform on the computer actions not allowed by the
user and can create copies of themeselves which are also able of creating their
own copies.
Classic virus
After a classic virus infiltrates into the system, it infects a file, activates in it,
performs its malicious action and then adds copies of itself into other files.