Just a few minutes ago I received a mail that looked very legitimate, it came from "Security Division" with the subject "Latest Internet Patch" when I opened it up I was greeted by the look and feel of emails Microsoft sends out:

this is the latest version of security update, the "September 2003, Cumulative Patch" update which fixes all known security vulnerabilities affecting MS Internet Explorer, MS Outlook and MS Outlook Express. Install now to protect your computer. This update includes the functionality of all previously released patches.

Of course I scanned the attachment and sure enough it was a virus, it's name was "Swen" F-Secure has rated this virus at Level 1: The highest warning a virus can get. Click this link to see an image (127kb) of the email I received. Also see MS01-020 for a fix to the vulnerability this virus makes use of. F-Secure (linked above) has free removal tools for this virus available for download.
Swen is a mass-mailer, which was first found on Thursday, September 18th, 2003. This rather complex worm uses several different techniques to spread and can, unlike most other e-mail worms, execute automatically when an infected e-mail message is received. Swen can also, in addition to e-mail, use IRQ chat, Kazaa networks and shared folders in local area networks to spread. Original article