I get really irritated when I am surfing quilting sites and get one of these same type of pop up... Never click on any kind of a pop up...somehow some of these have a way of sneaking past pop up blockers. They work really hard to make them look legit, and alarming too. Grrrr :evil:
If it really was from Microsoft, it would come to you as a update in the normal manner, to take care of a problem/virus/etc.