A security vulnerability exists in the Messenger Service that could allow arbitrary code execution on an affected system. An attacker who successfully exploited this vulnerability could be able to run code with Local System privileges on an affected system, or could cause the Messenger Service to fail. Disabling the Messenger Service will prevent the possibility of attack. This plugin determined by reading the remote registry that the patch MS03-043 has not been applied.

see http://www.microsoft.com/technet/security/bulletin/ms03-043.mspx