A Trojan horse is a program that disguises itself as an attractive, harmless, and useful program, when in reality it's a malicious application. Often confused with the computer virus, the Trojan is dissimilar because the methods of infection are different. A Trojan is a standalone program whereas a virus attaches to another application in order to replicate itself. Trojans can be delivered by email attachment, downloading shared files, or by hyperlinking to a website that initiates an automatic file transfer. If these damaging files are downloaded, installed and run, it can corrupt applications or harm the physical components of the computer. Trojans can act as a gateway for the hacker to pilfer information or monitor activity on a computer. Once the Trojan has infiltrated, it can steal information, destroy files, delete data and the hacker can take control of the computer. It can also send out unauthorized emails.

There are several ways to prevent and reduce the risk of becoming infected by a Trojan:

*Install a good firewall, anti-virus program and a spyware/adware scanner. There are several proprietary and/or free programs available. It's important to do the research and find one that is user friendly and has a successful record. There are also programs available that have been written specifically to combat Trojans. You might want to consider installing one of these as occasionally anti-virus applications do not effectively identify all Trojans (although they have improved over the last few years in Trojan detection). Make sure the data definition files are regularly updated in order to have the most current protection.

*Never download files from people you don't know and be cautious with files from people you do know. Verify all attachments with the sender to ensure legitimacy.

*Be alert to emails that arrive in your inbox. Trojans can come into the mailbox attached to an email disguised as an attractive game, screen saver, or as some other alluring application. It may appear to come from a friend, when in reality, a hacker has infected your friend and they unknowingly passed the vicious program on to you.

*Do not install/run a program that looks suspect. Many Trojans are difficult to detect because they are named similarly to legitimate programs. Familiarizing yourself with your applications can help reduce the risk of running a Trojan program. More importantly, since these programs may not always be openly visible, it's more effective to be vigilant and put restraints in to not install them in the first place.

*Do not visit suspect hyperlinks in emails and be cautious with websites you visit.
* Update the operating system with the latest releases and patches.
Once a Trojan is installed and executed, the file is activated and can cause destruction as a running program. While it does not replicate itself, just one click of the mouse can do sufficient damage and the exploiter who sent the Trojan can take over the computer at this point. After activation of a Trojan, the computer is opened up to many kinds of vulnerabilities and exploits. Using the preventative measures will help keep a computer Trojan-free. Education and learning how not to be "tricked" by the attractive Trojan is the strongest form of protection.

Learn more about this author, Leigh Goessl.
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