Antivirus software, fast, compatible, free?

[freedeanna]

I was wondering what antivirus software other users of Spybot S&D have found good. In particular I'm looking for something that doesn't use much CPU as this computer is getting a bit slow. I'm not even sure whether it would be safe to run without one if S&D is installed, or what security gaps S&D leaves. I just have Windows firewall running, on XP sp2. If possible I'd like to get free AV, although I'd pay a reasonable amount for something that is really fast (I mean the resident checking - I can wait for longer scans).

The background to this is that I had AVG for years now, but they've gone commercial-only with the latest version and I was so annoyed that they popped messages up in front of me to tell me to buy it that I went over to PCTools free antivirus (PCTAV). I was absolutely amazed how much faster everything ran and was delighted until I found that there were some problems. I've had a few different errors reported. During a spybot scan both it and PCTAV reported errors. PCTAV can go for 5 days and not update its sig files. It can appear to update them but not report it in the program, or vice versa, and generally gave me a very insecure feeling about it's design. AVG was obviously slowing everything down a lot, but it never seemed to cause a single error, and I never had a virus in that time, but they're not getting my custom for their spamming me!

I have now swapped to Avast, but unfortunately I've lost the speed advantage. I haven't tried yet, but maybe switching off some of the resident provider modules would help - but I don't know exactly what they all do or whether they only kick in if their needed and therefore don't slow things down on things that I'm not using (if you see what I mean). Besides, I don't much like the dumbed down sensitivity levels that don't actually describe what their differences are, just say "Normal - High - Custom", nor the spaceship CD player interface!

I'm wondering whether pctools threatfire is of any use as a replacement for an antivirus program, running with S&D. I read something about how we've all got so much security software running these days, the cure is becoming worse than the disease, and when I think about how much time I've spent on all this compared with the odd removal of a virus, I do wonder.

Your thoughts and experiences very much appreciated