"Symantec uncovered a new avenue that hackers could use to exploit a buffer overflow vulnerability in Microsoft Windows Messenger Service, one that, if packaged within a self-propagating worm, could spread across a network like wildfire."

The Windows Messenger Service vulnerability can be exploited by a single UDP broadcast, allowing a wholesale c compromise of all vulnerable systems on the targeted network. [Techweb]

To permanently Turn off the Messenger Service:
Click Start, and then click Control Panel (or point to Settings, and then click Control Panel). Double-click Administrative Tools. Double-click Services. Double-click Messenger. In the Startup type list, click Disabled. Click Stop, and then click OK. To turn it off permanently right click on properties then change startup type from Automatic to Manual or Disabled.