I am also very pleased with avast! Home Edition (free version). NOD 32 has long been regarded as the best paid-for anti-virus, but I read a user review of avast! Home from a person who used to use NOD 32 who switched to avast! Home, he/she said avast! Home is just as good as NOD 32. That is an awesome praise for a free product.
I use a layered computer security. I run BitDefender online scanner & it doesn't find anything 'cause avast! does it's job very good. Ad-Aware SE; ewido; Firefox; Microsoft AntiSpyware; Spybot Search & Destroy; SpywareBlaster; SpywareGuard; WinPatrol; XP SP2 auto-updates guard my computer from malware. Whenever I run my scans they never find anything because they do their jobs very well. ZoneAlarm is the best firewall. Nothing gets through that is bad.
I am very pleased with these free products. I don't see how the paid-for products could do any better. I call them my a to Z Security for avast! to ZoneAlarm with Ad-Aware SE; ewido; Firefox; Microsoft AntiSpyware; Spybot Search & Destroy; SpywareBlaster; SpywareGuard; WinPatrol & XP SP2 auto-updates in between.
I certainly am not belittling the paid for products. They have great convenience advantages that are not available in most of these free programs. I do respect everyone who buys the Pro versions, it is what keeps the providers in business.