Trojan horse

A Trojan horse, or Trojan, is software that appears to perform a desirable function for the user prior to run or install, but (perhaps in addition to the expected function) steals information or harms the system.

Purpose and uses

Adware

A destructive program that masquerades as a benign application. Unlike viruses, Trojan horses do not replicate themselves, but they can be just as destructive. One of the most insidious types of Trojan horse is a program that claims to rid a computer of viruses but instead introduces viruses onto the computer.

The term comes from the Greek story of the Trojan War, in which the Greeks give a giant wooden horse to their foes, the Trojans, ostensibly as a peace offering. But after the Trojans drag the horse inside their city walls, Greek soldiers sneak out of the horse's hollow belly and open the city gates, allowing their compatriots to pour in and capture Troy.

Security

Trojan may allow a hacker remote access to a target computer system. Once a Trojan has been installed on a target computer system, a hacker may have access to the computer remotely and perform various operations, limited by user privileges on the target computer system and the design of the Trojan .

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

Use of the machine as part of a botnet (e.g. to perform automated spamming or to distribute Denial-of-service attacks)

Data theft (e.g. retrieving passwords or credit card information)

Installation of software, including third-party malware

Downloading or uploading of files on the user's computer

Modification or deletion of files

Keystroke logging

Watching the user's screen

Crashing the computer

Anonymizing internet viewing

Trojan horses in this way require interaction with a hacker to fulfill their purpose, though the hacker need not be the individual responsible for distributing the Trojan horse. It is possible for individual hackers to scan computers on a network using a port scanner in the hope of finding one with a malicious Trojan horse installed, which the hacker can then use to control the target computer.

A recent innovation in Trojan horse code takes advantage of a security flaw in older versions of IE explorer and Google Chrome to use the host computer as an anonymizer proxy to effectively hide internet usage. The hacker is able to view internet sites while the tracking cookies, internet history, and any IP logging are maintained on the host computer. The host computer may or may not show the internet history of the sites viewed using the computer as a proxy. The first generation of anonymizer Trojan horses tended to leave their tracks in the page view histories of the host computer. Newer generations of the Trojan horse tend to "cover" their tracks more efficiently. Several versions of Slavebot have been widely circulated in the US and Europe and are the most widely distributed examples of this type of Trojan horse. .