The Microsoft Windows Malicious Software Removal Tool checks computers running Windows Vista, Windows XP, Windows 2000, and Windows Server 2003 for infections by specific, prevalent malicious software—including Blaster, Sasser, and Mydoom—and helps remove any infection found. When the detection and removal process is complete, the tool displays a report describing the outcome, including which, if any, malicious software was detected and removed.

Microsoft releases an updated version of this tool on the second Tuesday of each month, and as needed to respond to security incidents. The tool is available from Microsoft Update, Windows Update and the Microsoft Download Center. Because computers can appear to function normally when infected, Microsoft advises you to run this tool even if your computer seems to be fine. You should also use up-to-date antivirus software to help protect your computer from other malicious software.

Download this file at Microsoft's website.