I've installed stopzilla on my computers and like it pretty well. It actually catches spyware that Avast doesn't catch.
Before installing Avast, Stopzilla, and the freeware CCcleaner my computers were running slow again in 6 months. I spoke to a former friend of mine that worked for the IT department in my local newspaper. He told me the best way is to completely blow off your hard drive once every 6 months and do a fresh operating system install. He has his programs on a thumb drive for easy re-install.
I didn't want to bother with that so instead installed the 3 above programs and haven't had a problem since. Just like Pay Pal you have dissatisfied customers who hate it.
I also use this for all my transactions online that allow it. I like it also.
Product or Service Mentioned: Stopzilla Antivirus.
Reason of review: Good quality.
Stopzilla Pros: I have had excellent customer service and product reliablility.