Some users of Microsoft antimalware products have reported a performance issue with signature definition versions starting with 1.141.2400.0 (12/21/2012 1920 UTC).

The current definition files, since 1.141.2639.0 (12/27/2012 0625 UTC), resolve this issue. If you have a signature set in the affected range, please update to the current definition files.

Shannon Sabens
MMPC