Best way to be sure it's a legit Microsoft update is to just got to their update site and check. I used to do automatic updates but the last one actually crashed my machine. After paying the high price for XP, I would expect better updates at least. I have Firefox but someone figured how to send a nasty there too. Was just a trojan but it played havoc with some of my files. Now I use the latest AV/AntiSpyware from my own server. So far it has stopped the non-sense. But be aware, some hackers have actually put code in Web pages. One minute you're on a site and the next you've got a virus...ugh. Be careful where you surf. :)

Let me introduce you to my multiple personalities. :)
     BluEcho...Faery_Light...Faery_Souls.