It's 9 in the evening and, after a hard day's work, you settle in front of your PC to check the cricket scores. Suddenly, without any action on your part, a number of Web sites open up. One invites you to purchase a video of the best moments of the last World Cup. Another invites you to purchase Tendulkar tee shirts. Yet another promotes posters of the Sri Lankan squad, while a fourth site invites you to purchase sports goods with the Indian team's logo on it.

If this sounds familiar, it may be time to check your computer for spyware.

Spyware refers to computer programs that watch what you do on your PC, and then utilise this information for the benefit of some interested party. This monitoring is performed without the consent of the computer user. For instance, the program could track your browsing habits and, based on this, redirect you to certain sites where you are invited to purchase merchandise. Or, the program could watch while you type in your credit card number and forward this information to someone else. A few examples of spyware are CoolWebSearch, Internet Optimizer and BonziBuddy.

So, how did this little beast of a programme get into your computer in the first place?

You have only yourself to blame. Remember that cute dancing baby screensaver that your colleague sent you via e-mail? When you installed it, a not-so-cute program could also have been surreptitiously installed. Remember the time you clicked 'Yes' on the pop-up window that promised to optimise your Internet connection? It could be another possible infection.

Generally, spyware spreads by piggybacking on something desirable. The something desirable could be a screensaver, or the latest shareware program to manage your photo collection. It can also hijack your system when you click a link promising to take you to some oh-so-attractive Web site.

Once on your system, the spyware could do a whole lot of things:

~ It could display a lot of advertisements based on your browsing habits. If you're troubled by annoying ads that keep popping up at regular intervals, you have probably been infected.

~ The program could be monitoring important information like your passwords or credit card numbers. Once it has this information, it simply transmits it to the person who created the spyware program. I leave you to imagine what can be done with all this sensitive data.

~ The program could be modifying information that you send out. You have probably noticed links to some online stores on a number of sites. If you purchase anything from these stores, the owner of the site that directed you to a particular store gets a commission on your purchase. However, if you have spyware installed on your system, it makes it appear you were referred to the store by the spyware author's site. So, the spyware author gets the commission instead of the site that actually referred you.

~ The spyware program could also be responsible for controlling your data. In the Sony root-kit case, a program that was meant to prevent piracy was installed without the user's knowledge. This happened when the Sony music CD was inserted into the computer's CD-ROM drive. It installed software that then prevented the user from copying the CD.

Now that you know what spyware can do, it's time you learn how to keep your PC safe. The golden rule is: Never download anything from an untrustworthy source. This source could be a Web site that offers shareware, or an e-mail that offers you screensavers.

Periodically scan your computer with products like Microsoft's Windows Defender, Lavasoft Ad-Aware or Spybot-Search and Destroy. You could also use the anti-spyware features provided by your anti-virus product. It is important to remember that, when choosing an anti-spyware product, you should install a reputed program. There are numerous instances (like Spyware Cleaner) of spyware masquerading as an anti-spyware product.

Finally, keep downloading updates for your anti-spyware program. Stay informed, and you can stay safe.