What You Should Know About the Sasser Worm and Its Variants

Published: May 1, 2004 | Updated: May 2, 2004 - 3:30 P.M. Pacific Time

Software Affected by This Worm Microsoft Windows XP and Windows XP Service Pack 1 Windows 2000 Service Pack 2, Windows 2000 Service Pack 3, and Windows 2000 Service Pack 4 Software Not Affected by This Worm Windows XP 64-Bit Edition Version 2003 Windows Server™ 2003 Windows XP 64-Bit Edition Service Pack 1 Windows Millennium Edition Windows 98 Second Edition Windows 98 Windows NT® 4.0 Service Pack 6a Related Links Get More Technical Information About This Incident Glossary Terms Click the term to get the definition from our Security and Privacy Glossary. virus worm

Microsoft teams have confirmed that the Sasser worm (W32.Sasser.A and its variants) is currently circulating on the Internet. Microsoft has verified that the worm exploits the Local Security Authority Subsystem Service (LSASS) issue that was addressed by the security update released on April 13 in conjunction with Microsoft Security Bulliten MS04-011.

To protect your computer against Sasser and its variants, do the following:

Step 1: Enable a Firewall

Before you take other steps, make sure you have a firewall activated to help protect your computer against infection. If you have a hardware firewall in place for your home or workplace connection, or if you use the firewall included with Microsoft® Windows® XP, the Sasser worm is most likely blocked. If your computer has been infected, activating firewall software will help limit the effects of the worm on your computer. For comprehensive guidance to installing and enabling a firewall, see the Microsoft Protect Your PC site.

Step 2: Install the Required Update

To help protect your computer against the Sasser worm and its variants, you must first download and install security update 835732, which was released with Microsoft Security Bulletin MS04-011. You can find update 835732 on the Windows Update Web site listed in the Critical Updates and Service Packs section. You can also download and install this update manually from the Microsoft.com Download Center. To find the download for your operating system, refer to Technical Security Bulletin MS04-011.

Note  If you installed the updates for MS04-011 manually or through Automatic Updates before Friday, April 30, then you are already protected against this issue.

Step 3: Automatically Check For and Remove Sasser.A and Sasser.B

You can use this tool to search your hard disk for and try to remove Sasser.A and Sasser.B. To do so, click Check My PC for Infection.

Important  To use this tool, you must be running Windows XP or Windows 2000, and you must have already installed the update released with Microsoft Security Bulletin MS04-011.

Step 4: Review Additional Technical Resources

If the scanning and cleaning tool does not work for you, try using one of the free worm removal tools available at these antivirus software vendors' Web sites:

• Computer Associates
• F-secure
• Network Associates
• Norman
• Panda
• Sophos
• Symantec
• Trend Micro

If you prefer to remove the worm manually (for advanced users only), see the Microsoft Product Support Services (PSS) Security Response Team alert for technical guidance.

Step 5: Learn How to Protect Your PC

To help protect your computer against a wide variety of security threats, see Protect Your PC.