Microsoft and Windows has nothing to do with people who're constantly trying to "break" Windows OS. You should blame those individuals which don't have anything else to do, but ruining other people's lifes by releasing viruses, trojans and other nasties...
Believe me, even Unix can suffer similar problems, it's just there is not much people using it as it's the case with Windows, so it's not so interesting. Working as computer technician for the last 15 years, I've seen a lot of things... Windows are always good target, especially because many people hates Gates (for whatever reason). I personaly admires him. He knew how to make a business out of nothing... there is no business in the world that doesn't use all and any kind of ways to get where it aims... But, that's of course totaly off-topic. Microsoft is not an angel either, but holding it responsible for other people's crazy ideas (those which makes viruses) is not quite right.