At approximately 9:30 P.M. Pacific Time on Friday, January 24, Microsoft became aware of an Internet attack causing a dramatic increase in network traffic worldwide. Microsoft immediately began investigating the issue and learned of a worm targeting Microsoft. SQL Server-2000-based and MSDE 2000-based systems not updated with the appropriate security patches. This worm does not appear to attack the data of infected systems.
The "Slammer" worm is an Internet worm targeting un-patched SQL Server and MSDE systems resulting in a high volume of network traffic on the Internet.
The vulnerability that is exploited by this worm was first corrected by a Microsoft security patch in July 2002 and in subsequent cumulative patches, most recently in October 2002. These updates were also included in the recently released SQL Server 2000 Service Pack 3 (SP3) and MSDE 2000 Service Pack 3 (SP3). While systems that have installed any of these security patches are protected, Microsoft strongly recommends customers immediately follow the instructions for installing the most recent patch on TechNet, and begin evaluation and deployment of SQL Server 2000 SP3 or MSDE 2000 SP3 as appropriate.
The article continues at http://www.microsoft.com/security/slammer.asp