Most people have heard of computer viruses and the problems that they can cause. But there is another group of software that can be equally destructive. They are called Trojans or Trojan horses.

Trojans get their name from the famous Greek myths. In the story, the Greek army were besieging the city of Troy. Unable to break down the defenders they hit on an alternative plan. They built a wooden horse, which appeared to be a gift to the people of Troy. But once it was pulled inside the city gates, Greek soldiers hidden inside the wooden horse emerged and opened the gates.

A computer Trojan works in a similar manner. You may download an innocent looking program and install it on your computer. But at the same time a Trojan is installed that can cause harm.

For instance, you may decide that you want a new screen saver. You do a Google search and find a site offering nice free ones. When you download the screensaver, unknown to you a number of other programs have also downloaded in the background.

Trojans can cause a number of problems. Their payloads maybe designed to cause destruction to your computer files. Other Trojans download spyware that can be used in identity fraud. They can also be used as a way for hackers to get control of your computer. The hacker can then use your machine as part of a 'botnet' of compromised computers.

You can avoid your computer being taken over by following sensible online security measures. Install antivirus software on your computer and make sure it is up to date. This is usually also effective at detecting Trojans. There is also anti-Trojan capabilities in most antispyware software.

Avoid downloading files from unknown sources, and opening unknown attachments that you receive by email. You should also beware of file sharing sites that are notorious for being rife with spyware and Trojans.