Welcome to Trojan Library
A Trojan horse, or Trojan, is malware that appears to perform a desirable function for the user prior to run or install but instead facilitates unauthorized access of the user's computer system. The term is derived from the Trojan Horse story in Greek mythology.
A trojan may modify the user's computer to display advertisements in undesirable places, such as the desktop or in uncontrollable pop-ups, or it may be less notorious, such as installing a toolbar on to the user's Web browser without prior notice.
Trojans may allow a hacker remote access to a target computer system. Once a Trojan horse 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 horse.
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
Trojan horses in this way require interaction with a hacker to fulfil 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.
Due to the popularity of botnets among hackers and the availability of advertising services that permit authors to violate their users' privacy, Trojan horses are becoming more common. According to a survey conducted by BitDefender from January to June 2009, "Trojan-type malware is on the rise, accounting for 83-percent of the global malware detected in the world". This virus has a relationship with worms as it spreads with the help given by worms and travel across the internet with them.