I don't know if it's a virus, it may be more along the lines of hacking. A few weeks ago I was delightfully informed by a buddy of mine that I had sent out a Viagra ad to him. I checked with everyone in my contact list, and they all got it, too. :00hour
There wasn't much I could do -- I notified Hotmail and changed my passwords immediately, as well as the other online passwords I have that could cause some damage if hacked in to. Haven't had any issues since then.
The Hedge Files are on the net :scared