Keeping Windows free of malware

"After having installed an anti virus program on my pc on a year old installation of windows, i was surprised to find no virus' of any kind.

explain that"

You installed Windows a year ago, but you don't ever connect the computer to the internet and you install only pre-packaged commercial software?

That, or you're quite possibly the luckiest son of a b*tch to ever walk God's green earth, and I'd appreciate it if you'd send me 6 non-identical numbers (plus a, um...bonus number) between 1 and 49 please. Thanks!