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.
Types of trojan programs and their behavior are described in the table below.
Click to download table in PDF form