In the beginning I used a program called Grisoft AVG from free.grisoft.com but I kept getting update problems. The program just wouldn't finish updating. It kept saying that I had to restart the system before the update would finish, but no matter how many times I restarted my system, it just wouldn't finish.
Then came Anti-Vir from www.free-av.com. It was OK for awhile, but then it developed update issues and the Guard status was set to unknown.
And even after formatting my hard drive and reinstalling Windows XP from scratch (I had other problems as well), it didn't make any difference. So I dumped that and tried another program called PCTools Antivirus from www.pctools.com.
It had one annoying habit, everything I did, every click of the mouse, it would try to access or scan my floppy disk drive. Even when there was no floppy in the drive. It got so annoying, it was history the next day.
And now, AVAST!4 Home from www.avast.com/eng/avast_4_home.html . So far So good. I'll keep you updated.
Now you may be asking, Why not go to tech support to work out these problems? and the simple answer is - all of these programs are FREE, that usually means tech support is almost non-existent. Some offer forums but that means signing up for user names and passwords and/or scrolling through pages and pages of forum posts and hoping that someone else is having a similar problem.
The Paid for Versions, usually offer some direct support but either I cannot afford to pay for these versions or because of the online arrogance - (basically that means most online companies assume two things; one - that everybody has a super computer with the latest operating system that Microsoft decides to shove in your face - and two - that you have credit cards galore - I have none). I have had money to buy things online at times, but because the only option was to pay with a credit card - I was out of luck, the only consolation was, so where they.