In Vista we could choose the Anti Anti Virus. If we remain as standard users on 7 we can still.

I think a lot of people can do without an anti virus. The machine feels so snappy without one. As long as Windows Updates are never infected, and files from their official sources are safe, I should always be safe. I have not ran an Anti Virus since Vista. I run as a standard user and never get patches from the vendor themselves. We'll see if I get burned.

http://www.codinghorror.com/blog/archives/000803.html