A quick question ...

Just anti-virus? or do you need a firewall too?

Many of the larger brands have combination packages which are only slightly more expensive than their single anti-virus product. Symantec (i.e. Norton) has been producing anti-virus protection products for more than a decade -- that doesn't mean that their current product is the best; only that they have a long history from whence they have earned their expertice.

Other companies include McAfee, Trend, Sophos, Kaspersky LAB, Computer Associates, GRISoft, SOFTWIN, Dialogue Science, Frisk Software, IKARUS, GeCAD RAV, and VirusBuster -- and probably a dozen more of which I am unaware.

Furthermore, you should make sure your operating system (OS) is fully patched as many viruses, worms and trojan horses try and exploit weaknesses therein.

A good anti-virus program will help insure that your computer is only infected for a short period of time ... a good firewall will help insure that your computer is extremely difficult to infect.

Only you can determine what your needs are ...