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Trojan - technical definition

Named after the Trojan Horse of ancient Greek history, it is a particular kind of network software application developed to stay hidden on the computer where it has been installed. As with worms, Trojans generally serve malicious purposes and are in the Â“malwareÂ” classification. Trojans sometimes access personal information stored on home or business computers and then send it to a remote party via the Internet. Alternatively, Trojans may serve merely as a back door application. Trojans can also launch DoS attacks.

A combination of firewalls and anti-virus software should be used to protect networks against Trojans.

New Trojans are released on a frequent basis. For example, on March 3, 2005, security experts at McAfee and SophosLabs issued alerts of a new Trojan virus called Troj/BagleD1-L. This Trojan tries to prevent various security applications (such as anti-virus and firewall software) from working by renaming files belonging to security applications so that they can no longer load. It then attempts to block access to a range of security-related Websites by altering the Windows HOSTS file. The virus is said to arrive on email messages having a ZIP attachment. After it is opened, the ZIP attachment includes a program file named Â“docÂ—01.exeÂ” or Â“prsÂ—03.exeÂ” or some other name. If the program inside the ZIP attachment is opened, the Troj/BagleD1-L attempts to connect to one of many Websites to download more code.

About, Inc. Trojan. [Online, 2004.] About, Inc. Website. http://compnet working.about.com/cs/worldwideweb/g/bldef_trojan.htm; In Brief. Security Experts Fear New Trojan on the Loose. The Globe and Mail, March 3, 2005, p. B10.

See Trojan in Computer

A program that appears legitimate, but performs some illicit activity when it is run. It may be used to locate password information or make the system more vulnerable to future entry or simply destroy programs or data on the hard disk. A Trojan is similar to a virus, except that it does not replicate itself. It stays in the computer doing its damage or allowing somebody from a remote site to take control of the computer. Trojans often sneak in attached to a free game or other utility. For information about various Trojans that are spread on the Internet, visit the Lockdown Corporation at www.lockdowncorp.com. See rootkit, RAT, Back Orifice, NetBus, PrettyPark, Talking Trojan and virus.

The Trojan Horse
Trojan comes from Greek mythology, in which the Greeks battled the Trojans (people of Troy). After years of being unable to break into the fortified city, the Greeks built a wooden horse, filled it with soldiers and pretended to sail away. After the Trojans brought the horse into the city, the Greek soldiers crept out at night, opened the gates of Troy to the returning soldiers, and Troy was destroyed.