I have tried several free anti-virus programs and have found that most of them just don't cut the mustard.
I prefer one that you make a one-time payment and can use it on as many computers as you want to, but if you have to pay a minimum yearly subscription, that's okay, too. PCW rated 5 AV programs from best to worst-
G-Data, Symantic Norton AV 2010, Kapersky AV 2010, Bit Defender AV 2010, and Panda AV Pro 2010. Users nearly 2-1 didn't like G-Data.
I used Avg for many years and it didn't catch all problems. Then I went to Avira. When working on other people's computers, I've found Norton AV a bear to remove. Plus, they want to keep charging on your credit card. Any feedback on NOD?