the sasser worm attempts to exploit a known vulnerability in Windows 2000 and Windows XP. Microsoft has come up with an update to address this problem.

So in addition to running Anti Virus software on your computer and keeping it updated, you also need to make sure your Windows operating system is up to date.

That can be done by going to the website below and letting it scan your computer and then download and install the recommended patches.

http://v4.windowsupdate.microsoft.com/en/default.asp

Cheers!
Bill