Microsoft has re-released one of last week's security updates after realising the patch it had issued didn't do the job.

"After we released MS08-030 we learned that the security updates for Windows XP SP2 and SP3 might not have been fully protecting against the issues discussed in that bulletin," Christopher Budd, a spokesman for the Microsoft Security Response Center (MSRC), said. "As soon as we learned of that possibility, we mobilized our Software Security Incident Response Process (SSIRP) to investigate the issue."

MS08-030 was part of a group of seven security updates that patched 10 vulnerabilities in Windows and other Microsoft software. Called out by several analysts last week as the most interesting fix of the bunch, MS08-030 was supposed to plug a hole in Windows' implementation of Bluetooth, the short-range wireless protocol. The update was one of three pegged "critical," the highest threat ranking in Microsoft's four-step scoring system.

Although the patch offered last week for Windows Vista and the 64-bit versions of Windows XP did the trick, the fix for the 32-bit editions of XP, including the new Service Pack 3 (SP3), did not, said Budd. He also promised that Microsoft would find out how the non-patching patch made it through the company's testing.

Human error, he added, is the likely cause. "As part of our standard process, we're beginning an investigation into how this happened," Budd said in a short entry to the MSRC's blog today. "We're just starting this investigation, but early on, it appears that there may have been two separate human issues involved. When we're done with our investigation, we'll take steps to better prevent it in the future."

Microsoft has had to re-release patches before. It most recently went back to the drawing board in March, when it was forced to re-issue a flawed update that had caused some versions of its Excel spreadsheet to make maths mistakes.

The revised MS08-030 bulletin stated that the new patch for Windows XP has been seeded to the usual Microsoft distribution channels, including Automatic Updates, Windows Update and Windows Server Update Services (WSUS).