I use my pc 12+ hours a day, haven't installed any 3rd party antivirus software since 2005, and haven't encountered a single problem, because I know what I'm doing. I think all people who read ycombinator should be able to do the same.
I haven't used an anti-virus in all of my 20+ years of computering. I've been hit with some minor infections (mostly from torrents, which I knew was not safe). But that's it.
