Microsoft has warned enterprises of glitches involving a security update issued last week. A patch designed to fix a flaw in Windows middleware components (MS05-051.mspx) creates system instability in environments with modified Access Control List (ACL) settings.

In a statement, Microsoft said it is "aware of reports of isolated issues after deployment with Microsoft Security Bulletin MS05-051. We are working with a limited number of affected customers to help resolve these issues". It's unclear how many users are affected by the glitch. Problems arising from the update can range from leaving users unable to log on after the patch is applied to a blank screen after the update. But not applying the update leaves systems vulnerable to a critical security glitch that security firms warn is ripe for exploitation by an internet worm.

That leaves sys admins damned if they don't and (possibly) screwed if they do and in an unenviable position where extra testing would seem to be the only sensible approach. ®