For any Internet connected PC or network, a regularly updated anti-virus program is a must. Standard Anti-virus software works by examining individual files within your hard disk for telltale signs, or signatures, of specific virus programs. A program using this method, called 'exact detection', is only as good as its database of known virus definitions, which is why it is important to update frequently.

The major anti-virus software companies used this approach exclusively, until recently when they have begun flirting with the other major method of virus detection, heuristic detection. This method does not define a virus by matching the exact pattern of data that makes up its signature, but rather by observing its behavior.

or example, a heuristic (Greek for 'to find') anti-virus program might be instructed to watch for non-authorized programs that attempt to make changes to the computer's registry, or to access system files. There are many different methods of implementing heuristic anti-virus software, but that is really beyond the scope of this article. The major reason behind the partial adoption of heuristic anti-virus methods by the big companies such as Symantec (makers of Norton Antivirus) is the success in recent years of mass-mailing worms. Worm are computer viruses which replicate themselves through email.

The incredibly fast rate of infection seen in cases such as the vbs.loveletter worm (which you may recognize as the 'I love you virus'), Anna, and recently the w32.bugbear worm took the major anti-virus manufacturers off-guard. They were not able to release virus definitions fast enough to prevent major distribution of the aforementioned viruses.

The major virus protection companies are now incorporating features into their software which will allow it to detect behavior characteristic of these mass-mailing worms, without necessarily having a virus signature for them, hoping to head off such outbreaks in the future... at least among paying customers.

For home use, an antivirus software package is highly recommended. Symantec's Norton Antivirus and MacAfee's VirusScan are two leaders in the area, but the brand name does not matter as much as the frequency of the virus updates which the company offers. There are several other reputable packages available besides these, especially for the business world.

For software such as this, which needs to be frequently updated by the manufacturer, expect to pay a subscription fee in the future. Most home anti-virus software ships with a one-year subscription to the company's updating service, after which you will need to renew.

If you suspect you already have a virus on your computer, and you either do not have access to an anti-virus program or the one you do have does not seem to be doing the job (not too surprising, as many viruses include disabling the functionality of major anti-virus checkers as part of their payload), all is not lost. There are resources available on the Internet for identifying and eliminating viruses manually.

As a start, you can go to www.sarc.com This is Symantec's public virus threat information website. If you use the encyclopedia, you can find information and removal tools or instructions for many recent viruses.

On the same page there is a link to the Symantec security check, which will scan your computer and identify any viruses that fit a known signature, using their latest definitions. It will not remove them of course, but it's a start. Then you can look them up in the virus encyclopedia for removal instructions.