Elsewhere, the company acknowledged that the original patch didn't do its job. "Today, we pulled the update because we found it does not address the underlying issue effectively," said Jerry Bryant, group manager for the Microsoft Security Response Center (MSRC), in a post to the Wednesday.

Microsoft has stopped distributing the update through its various update mechanisms, including Windows Update and the -grade Windows Server Update Services (WSUS). Bryant said that Microsoft plans to re-release the patch next week.

"It's interesting why they chose to pull the patch," said Andrew Storms, director of security operations at nCircle Network Security, in an instant message. "If it doesn't fix the bug, does it have some kind of unexpected outcome? Otherwise, why simply pull it all together and leave a gap in coverage?"

The original update patched a single critical vulnerability in Windows 2000 Server's handling of network packets when running Windows Media Services.

MS10-025 was one of 11 security updates that Microsoft shipped April 13 to in Windows, Office and Exchange. It was one of five updates marked "critical," Microsoft's highest threat ranking.