What is a Trojan Horse?

Named for a giant horse that was supposed to be a gift but was filled with the Greek army, a Trojan horse program can be just as deceptive. The story goes that the Greeks gave the Trojans a huge wooden horse as a peace offering. The citizens of Troy accepted the gift, brought the horse inside the city, threw a victory bash, then went to bed. It wasn't until the Greek soldiers had set the city on fire that they realized they'd been had. A Trojan horse that affects computers can contain some nasty surprises as well. It can damage, delete, or destroy important files.

A Trojan horse may actually appear to be a useful application, which is why so many unsuspecting people download them. It might be disguised as a program intended to rid your computer of viruses, yet actually be used to infect your system instead. While the terms "virus" and "Trojan horse" are frequently used interchangeably, they are actually quite different. A virus replicates itself, while a Trojan horse does not.

Once a Trojan horse is activated, it can access files, folders, or your entire system. Commonly, Trojans create a "backdoor" or a "trapdoor," which can be used to send your personal information to another location. To protect your system, extensive anti-virus software is a good first step. Choose a program that looks for Trojan horses and worms as well as viruses, and make sure it updates definitions for each frequently. Also, make sure your anti-virus scans email, and gives an alert or automatically deletes any message that contains suspicious code, even if the code is not specific malware that the program has already identified.

The most effective option for protecting against a Trojan horse may be installing a firewall if you do not already have one. A good software firewall is usually the best type for a personal computer. It can be configured to keep intruders out while also keeping your system, or programs within your system, from sending out personal or confidential data.

If you are unsure, test drive a trial version of a firewall or download a free one to check it out. Run it for one day and examine the log file. You'll be shocked by the amount of information that goes in and out of your computer in twenty-four hours. You may even detect a Trojan or other malware that got past your anti-virus, since they are frequently difficult to detect.