W32.Swen.A@mm is a mass-mailing worm that also attempts to spread through file-sharing networks such as KaZaA and IRC and will attempt to de-activate antivirus and personal firewall progs running on your PC.
I got two copies of these this morning around 5:00am one from microsoft with an attachment, norton antivirus detect1.txt and another about an email that could not be delivered. In both cases the attachment had the worm. DO NOT open the attachment. Delete it.
It was kind of funny.I was watching the news and they said something about the new worm and lo and behold when I checked my email there they were. I have NWS2003 and NIS2003 but the emails still showed up.