I haven't had a virus affect me since the 90's and I only run Microsoft operating systems

I don't have any anti-virus installed, every couple months I do an online virus scan.
I am going to install this beta though, I like trying new software & I like that there is a 63bit version. I will disable it from active protection and auto-startup though, I hate having stuff running that i don't need.
http://www.microsoft.com/security_essentials/