SQL Slammer is a computer worm that first appeared in the wild in January 2003, and caused a denial of service condition on tens of thousands of servers around the world. It did so by overloading Internet objects such as servers and routers with a massive number of network packets within 10 minutes of its first emergence.
The worm exploits a buffer overflow vulnerability in Microsoft SQL Server 2000 or MSDE 2000 by sending a formatted request to UDP port 1434. After the server is infected, it attempts to spread rapidly by sending the same payload to random IP addresses, causing a denial of service condition on its targets. This vulnerability was discovered by David Litchfield several months before Slammer first launched. Accordingly, Microsoft released a patch, but many installations had not been patched before Slammer’s first appearance.