Users who applied the update last week do not have to uninstall it, but Microsoft urged users to review the workarounds and additional defensive measures it outlined earlier to protect themselves until it reissues the patch. The company also recommended that systems running Windows Media Services be protected by a firewall.

By Storms' recollection, this is the first time that the company has retracted an update without an immediately-available revamp of the fix. Microsoft was not immediately able to confirm that the move is a first.

"We have to give Microsoft credit for the transparency," said Storms, talking about the admission that the update didn't quash the bug. "Honestly, they are a bit lucky [that] the event happened on a bug with little market share. If this were or Internet Explorer, I highly doubt they would pull the plug on the patch without having the new one ready to issue," he said.

As Storms alluded, Windows 2000 powers relatively few PCs. According to the most recent data from Web analytics company NetApplications, the 10-year-old Windows 2000 accounts for just 0.6% of all in-use operating systems, less than a hundredth the share of Windows XP.

has reissued patches in the past. In 2008, for example, the company re-released four different security updates for various reasons, including what it called that forced it to reissue a fix for a Bluetooth bug in Windows XP.