System information

Threats to computer security 21
Unlike worms and viruses, trojan programs do not create copies of themselves.
They sneak into a computer, for example, via e-mail or using a web browser
when the user visits an "infected" website. Trojan programs are launched by the
user and start performing their malicious actions as they run.
The behavior of different trojan programs in the infected computer may differ.
The major functions of Trojans are blocking, modification and erasing of data,
disruption of the operation of computers or computer networks. Besides, Trojan
programs can receive and send files, run them, display messages, access web
pages, download and install programs and restart the infected computer.
Intruders often use "sets" consisting of various trojan programs.
Types of trojan programs and their behavior are described in the table below.
Table 2. Types of trojan programs by behavior on the infected computer
TYPE
NAME
DESCRIPTION
Trojan-
ArcBomb
Trojan programs -
archive bombs
Archives; when unpacked, they increase
to a size that disrupts the computer's
operation. When you attempt to unpack
this archive, the computer may start
working slowly or "freeze" and the disk
may be filled with "empty" data. "Archive
bombs" are especially dangerous for file
and mail servers. If an automatic incoming
information processing system is used on
the server, such "archive bomb" can stop
the server.
Backdoor
Remote
administration
Trojan programs
These programs are considered the most
dangerous among Trojan programs;
function-wise they remind of off-the-shelf
remote administration programs. These
programs install themselves without the
user's knowledge and give up to the
intruder remote management of the
computer.