I understand that there are many opinions in regard to the "best" free AV products. Some people recommend Avira AntiVirus; others recommend Avast or AVG. Apparently each of these three products have their pros and cons as well as fervent supporter.
I had been happily using Avast for the last couple of years at least until the 'false positive' problem that occurred a couple of weeks ago. Prior to that Wednesday, my computer (2.80 GHz, 3MB RAM, Windows XP SP3, dual-core processor) with Ad-Aware, Avast, Comodo Firewall, PC Tools Spyware (no AV), Prevx and Immunet Protect loaded was working fairly well and fast.
After the 'false positive' debacle, I had to reformat my drive and reinstall everything. As soon as I was done reinstalling everything (to the exact same configuration then before), I noticed a great degradation in my computer's performance in terms of speed as long as Avast was running. With Avast disabled, everything would once again work well and fast. I don't know what the cause of the problem is but I know that with Avast running my computer slows to a crawl.
I tried Avira but I did not like their 'upgrade' message constantly popping up. I was then 'forced' to switch to AVG. Even with its limitations, AVG is better than no protection.
If anybody has a better solution, let me know.