Virus FAQ - AVG

http://www.avg.com/gb-en/faq.pnuid-faq_v3_virus_8_root 
What is a trojan horse


A Trojan horse is a malicious application that is designed to enable remote access to the target computer system.  Trojan horses cannot automatically replicate themselves.  After installing a Trojan horse, it is possible for hackers to access the computer remotely and perform various operations.  The operations that can be performed are limited by the design of Trojan horse and by user privileges on the attacked operating system.  Common operations include:

• Modification of files
• Data theft (personal information, credit card information, used passwords...)
• Keyboard input logging
• Installation of other software (including malware)

Generally, most Trojan horses can be detected and removed by AVG. The Identity Protection component (available in some AVG editions) can also protect the computer against various types of malware, including Trojan Horses, based on behavioral monitoring of running processes.

Trojan horses can be also removed manually, but this requires complete information on how the particular Trojan horse operates. If you have any doubts or questions regarding Trojans, please do not hesitate to contact AVG Customer Services as described in FAQ 2216.