A recent increase in malicious activity on the Internet, including the development of attack tools and exploit code, has resulted in an automated attack against computer users in the form of a worm identified as "W32.Sasser.worm" ("Sasser"). Through this worm, the attacker is attempting to exploit systems that are not protected against the Local Security Authority Subsystem Service (LSASS) vulnerability, which is mitigated by the use of a firewall and fixed in Microsoft Security Update MS04-011 on April 13, 2004. There is additional malicious activity in the form of variants of a worm known as "Agobot" (or "Agrobot"), which similarly seeks to exploit systems not protected by a firewall or the installation of MS04-011.

Microsoft is working closely with law enforcement authorities, including the Northwest CyberCrime Taskforce, a joint effort between the FBI and U.S. Secret Service, to forensically analyze the malicious code in Sasser and Agobot, to identify and bring to justice those responsible for this malicious activity. The investigation is ongoing, and questions about the investigation should be referred to the Northwest CyberCrime Taskforce.

At the same time, Microsoft is working closely with the anti-virus community and other industry partners to help protect our customers. Customers using a firewall-- including the firewall in Windows XP, as well as third-party hardware or software firewalls -- are generally protected against the Sasser and Agobot threats. Customers can protect against these attacks by first ensuring that their firewall is in place, and then installing Microsoft Security update MS04-011 immediately. The MS04-011 security bulletin is available as a free download at www.microsoft.com/technet/security/bulletin/ms04-011.mspx or users can use Windows Update to access the latest security update.