In short, a Trojan horse virus represents a malware that infects a system to help its author illegally gain access to a computer for various reasons, including stealing personal information, obtaining passwords and detailed data of bank accounts. Trojan horses differ from common computer viruses and worms by the fact that they do not replicate themselves.
It is rather easy to get infected by the Trojan horse virus. There are several ways using which Trojan horse viruses manage to penetrate a computer. For example, a Trojan horse can be hidden in an e-mail attachment, freeware and shareware programs. Probably the most popular way of getting infecting is visiting websites that feature a Trojan horse, with the latter being downloaded without any notice. It is highly advised to regularly screen your computer and remove Trojan horse using automated anti-spyware or anti-Trojan software.
A Trojan horse virus could be included in a program that at first sight appears to be rather harmless. With just a small Trojan horse virus, the hacker can install other computer viruses on the infected computer or enter the system through the back door. Although there are several types of Trojan horse programs, all of them perform (more or less) two main functions: watching and monitoring, and stealing and hijacking.
Watching and Monitoring Trojan Horses
These Trojan horses try to gain as much information as possible about the user and his or her surfing habits. Hacker who monitors the Trojan horse will then attempt to use the gathered information for various purposes, like selling the data to parties that might be interested in it. Often such Trojan horse viruses are written carefully and cannot be easily spotted on the infected system, because the longer a Trojan horse resides in a computer the more information its developer receives.
Stealing and Hijacking Trojan Horses
These Trojan horses are somewhat more dangerous. Hackers use such viruses to carry out much more dangerous actions. Often these Trojan horses attempt to gain detailed data on banking passwords. In addition, a Trojan horse can be used to run other software programs and launch a Denial of Service Attack. Today DDOS attacks represent a big business with individuals or a group of people providing such services in return for a financial motivation. link....