O.K. here is my Smart Ass remark. If you were using a properly designed Operating System, then you would not have to use any sort of Anti-Virus software. The fact that you have to add this software, and probably pay a yearly registration fee to boot, indicates that the underlying operating system is flawed to begin with. How many OS-X (Mac) or Linux users have these sorts of problems?
Microsoft, was so affective at keeping competition out of the Marketplace by breaking numerous anti-trust laws, that no one was the wiser regarding other options. I would say that Desktop versions of Linux are very usable at this point. I'm running Ubuntu on my laptop.