Well, at least it is FREE. It wouldn't surprise me if Microsoft charged to keep out the viruses that are exploiting loopholes in THEIR OWN OS! You are being more charitable towards Microsoft than I feel. If Microsoft was truly gung-ho on security, they should start by tightening up the security settings for new Windows installations....Or perhaps they have finally turned the corner with Windows 7.
Oh but they did! They put it on the user to answer all the dialog boxes every time you go to do something on the computer. You really don't expect M$ to write code to tighten up security that would eat into their profit's.