Being at least half-decent in the way I use my Windows computers + AVG free edition -> one reportedly infected file in the past decade+
I can't remember what MSE does, I may have some of that opened up as well (windows firewall and a couple other things).

Then again, I pretty much use Windows these days only for videogames. I've transitioned to linux for all the other computational problems of my life, and with that the virus/malware problem has vanished.