The term "virus" is widely applied to programs that can infect your computer without your knowledge or consent. In fact there are several distinct categories only one of which is properly called a "virus", but this distinction is perhaps only of interest to techies. In addition to straight-forward viruses there are "Worms", "Trojan Horses" and "Spyware".

Viruses usually arrive as an e-mail attachment which the user inadvertently opens. Virus writers use some well-tried ploys to dupe users into doing this, despite frequent advice to be careful. They use plausible-sounding subject lines, for example, or the virus uses e-mail addresses from the infected machine to send itself to someone else, usually in the address book. That way, someone will receive an e-mail from someone they know with a subject line that dupes them into thinking it is "safe" to open it.

You should adopt a strict anti-virus policy:

Because they tend to arrive mostly via e-mail some people tend to lump them together with spam, treat them as one problem and then get all confused when they read what appears to be conflicting information. Spam is a serious nuisance, but Viruses can cause damage to your computer system.

Worms can arrive as e-mail as well. They can propagate by sending our masses of e-mails with copies of the Worm attached, or by using the computer's own connection to the Internet to look for other vulnerable computers and infect them directly.

Trojan Horses, on the other hand, and some types of viruses, are generally downloaded from illicit web sites. Needless to say there are some web sites you should not visit and some types of files you should not download. If you think it may not be legal, the chances are there might be a nasty pay-off as well. Stick to legitimate businesses and you should be okay.

The way to protect yourself from Worms and Trojan Horses is by running a Firewall. This is a special program that prevents other unauthorised programs from accessing your computer while you are connected to the Internet, or any other network. Personal Firewalls are available stand-alone but are often bundled together with most versions of anti-virus programs for a better deal.

Spyware or Malware as it is sometimes known, is a special type of virus that monitors your use of your computer and sends that information to a third party. For example, it can monitor the ink levels in your desk-jet printer and when it gets low enough will pop-up a window to take you to a site that sells ink cartridges. Other forms can be downright dangerous and could steal your credit card numbers as you type them into a legitimate on-line shop. It then sends that data to a third party.

VIRUS TIP 1 Only open an attachment if it is from someone you know AND it is something you are expecting AND the subject description, the covering note and the file name all make sense. If in doubt CHECK with the sender.

VIRUS TIP 2 Update your anti-virus program before you download your e-mail for the first time each day. That way it will be as up-to-date as it can be in case there is a new-variant virus waiting for you to download.

VIRUS TIP 3 Keep your Windows software up-to-date. You need to eliminate all vulnerabilities on your computer in case a virus or something does get through, a lot of hackers are looking to exploit them. The Microsoft sites have a number of helpful pages:

Windows Live "One Care" - free on-line safety scan from Microsoft

Microsoft Update - checks most MS products

MS Office scanner - checks your version of Office for updates

Windows XP Live Update - checks your version of XP