Trojan horse virus Computer

Trojan horse virus Computer
A Trojan horse (sometimes shortened to trojan[n 1]), is non-self-replicating malware that appears to perform a desirable function for the user but instead facilitates unauthorized access to the user's computer system. The term is derived from the Trojan Horse story in Greek mythology.

Trojan horses are designed to allow a hacker remote access to a target computer system. Once a Trojan horse has been installed on a target computer system, it is possible for a hacker to access it remotely and perform various operations. The operations that a hacker can perform are limited by user privileges on the target computer system and the design of the Trojan horse.

Operations that could be performed by a hacker on a target computer system include:

Use of the machine as part of a botnet (i.e. to perform spamming or to perform Distributed Denial-of-service (DDoS) attacks)
Data theft (e.g. passwords, credit card information, etc.)
Installation of software (including other malware)
Downloading or uploading of files
Modification or deletion of files
Keystroke logging
Viewing the user's screen
Wasting computer storage space
Trojan horses require interaction with a hacker to fulfill their purpose, though the hacker need not be the individual responsible for distributing the Trojan horse. In fact, it is possible for hackers to scan computers on a network using a port scanner in the hope of finding one with a Trojan horse installed, that the hacker can then use to control the target computer.[1]

A trojan differs from a virus in that only a file specifically designed to carry it can do so.

Refer to http://en.wikipedia.org/wiki/Trojan_horse_(computing)