System information

Threats to computer security 17
MALICIOUS PROGRAMS
Malicious programs (“malware”) are created specifically to inflict harm on
computers and their users: to steal, block, modify or erase information, or to
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 (Viruses_and_Worms) (see page 17) can create copies of
themselves, which in turn spread and reproduce again. Some of them run
without the user's knowledge or participation, others require actions on the user's
part to be run. These programs perform their malicious actions when executed.
Trojan programs (Trojan_programs) (see page 20) do not create copies of
themselves, unlike worms and viruses. They infect a computer, for example, via
e-mail or via a web browser when the user visits an “infected” website. They
must be launched by the user, and perform their malicious actions when run.
Malware utilities (Malicious_tools) (see page 26) are created specifically to inflict
damage. However, unlike other malware programs, they do not perform
malicious actions as they are run and can be safely stored and run on the user's
computer. They have functions which hackers use to create viruses, worms and
Trojan programs, to arrange network attacks on remote servers, hack computers
or perform other malicious actions.
VIRUSES AND WORMS
Subcategory: viruses and worms (Viruses_and_Worms)
Severity level: high
Classic viruses and worms perform unauthorized actions on the infected
computer, including replicating and spreading themselves.
Classic virus
After a classic virus infiltrates the system, it infects a file, activates itself,
performs its malicious action, and adds copies of itself to other files.
Classic viruses reproduce only within the local resources of the infected
computer, but cannot independently penetrate other computers. Distribution to