a worm that spreads over network connections (not email) without any user interaction

The Sasser is a computer worm that affects computers running vulnerable versions of the Microsoft operating systems Windows XP and Windows 2000. Like other recent worms, Sasser spreads by exploiting the system through a vulnerable network port. Thus it is particularly potent in that it can spread without the help of the user, but it is also easily stopped by a properly configured firewall, or by downloading patches from Windows Update http://windowsupdate.microsoft.com.