System information

Threats to computer security 23
TYPE
NAME
DESCRIPTION
Trojan-
Downloaders
Trojan programs-
downloaders
These programs access the intruder's web
page, download other malware programs
from it, and install them on the user's
computer. They can either store the name
of the downloadable malware program
filename in their own code, or receive it
from the web page they access.
Trojan-
Droppers
Trojan program-
droppers
These programs save programs
containing other Trojan programs on the
computer's disk and then install them.
Intruders can use Trojans-Droppers in
different ways:
 to install malware programs without the
user's knowledge: Trojans-droppers
either do not display any messages, or
display false messages, for example,
notifying about an error in an archive or
about using the wrong version of the
operating system;
 to protect another known malware
program from being detected: not every
anti-virus program can detect a
malware program located inside a
Trojan-dropper.
Trojan-
Notifiers
Trojans-notifiers
They notify the intruder that the infected
computer is connected; and then transfer
information about the computer to the
intruder, including: IP address, number of
an open port or the e-mail address. They
communicate to the intruder using a
number of methods including e-mail, FTP,
and by accessing the intruder's web page.
Trojan-notifiers are often used in sets of
complementary Trojan programs. They
notify the intruder that other Trojan
programs are successfully installed on the
user's computer.