Are you a Windows Vista, XP or Windows Server 2003 user that has lost patience with updating your system every time Microsoft tells you to? Then pay attention; you might be vulnerable to the Downadup worm, which is spreading like wildfire among unprotected PCs. According to Computerworld, 9 million computers have been infected in the last two weeks alone.

The worm exploits a vulnerability in Windows that was recognized by Microsoft in October of 2008. The company issued an update at that time to address this problem, but apparently millions of users didn't get the message, or chose to ignore it.

The worm allows the infected computer to be hijacked and used in nefarious ways such harvesting personal info or contributing to denial of service attacks.

Symantec, the company behind Norton Anti-virus, deems this "one of the most prolific worms we've seen in years", which has "an extremely large infection base that could do a lot of damage." To safeguard yourself, make sure you've installed the update, and run Microsoft's Malicious Software Removal Tool.