What is a Trojan

According to legend, the Greeks won the Trojan war by hiding in a huge, hollow wooden horse to get into the fortified city of Troy. In today's computer world, a Trojan horse is defined as a "malicious, security-breaking program that is disguised as something benign" such as a screen saver, game.

Trojan horses are the most destructive and dangerous species of computer viruses. Most of them are resident stealth viruses, which means that they are constantly in the memory of your PC and can not be detected using common ways.


Files attached to your email and files you download from the internet are easiest way to become infected. Any file you download can contain a trojan.


When opened, it would unleash a slew of problems, such as sending itself to everybody on your email address book or IRC channel, erasing or modifying your files, and downloading another Trojan horse program designed to steal your passwords. Many Trojan horses also allow crackers (aka "hackers") to take over your computer and "remote control" it, such as to take over your IRC channels or use your computer to perform denial of service attacks like those that disrupted web sites of Yahoo and Amazon.

When the infamous Back Orifice 2000 is installed on a Windows-based computer, the computer can be remotely controlled by another user. Although remote control software is not malicious in and of itself, Back Orifice 2000 is intended to be used for malicious purposes, and includes stealth behavior that has no purpose other than to make detection of the program difficult.

The remote user will be able to read, write, delete and transfer files to and from the affected machine. If they use a plug-in supplied with Back Orifice 2000 they will be able to see what is on the screen of the affected machine and also take control of the mouse and keyboard. The affected machine can also be configured to be an HTTP file server allowing anyone with a web browser to transfer files to and from it.

The remote user could have made changes to your system, including but not limited to the following:

o Stealing or changing passwords or password files
o Installing remote-connectivity host software, also known as backdoors
o Installing keystroke logging software
o Configuring of firewall rules
o Stealing of credit card numbers, banking information, personal data, and so on
o Deletion or modification of files
o Sending inappropriate or even incriminating material from a users email account
o Modifying access rights on user accounts or files
o Deleting information from log files to hide such activities