Microsoft offered a group of antivirus definition updates in SCEP and FEP (System Center Endpoint Protection (SCEP) and Forefront Endpoint Protection (FEP) ) that crashed XP and Server 2003 systems worldwide.

Sysadmins complained on TechNet that large numbers of XP machines were screwed after installing the update. The only way to fix the issue was to uninstall the update. One system admin said he saw 750 machines affected while another complained of a screwed network of 3,500 PCs.

“Seems like an engine and/or signature update to FEP in combination with a specific setting within FEP crashes FEP, which then knocks out the affected computer from the network.”

A Microsoft spokesman said that the latest signatures would automatically resolve the issue.