According to users who posted complaints to Microsoft's support forum, after installing the update, one of 13 released Tuesday, their machines refuse to start up.
Instead, their systems shudder to a stop at the blue screen which in Windows indicates a serious software error and crash.
"We stopped offering this update through Windows Update as soon as we discovered the restart issues," said Jerry Bryant, a senior manager with the Microsoft Security Response Center (MSRC).
Bryant also said that Microsoft was digging into the problem.
"Our initial analysis suggests that the issue occurs after installing MS10-015 (KB977165)," he said.
"However, we have not confirmed that the issue is specific to MS10-015 or if it is an interoperability problem with another component or third-party software."
He also downplayed the extent of the blue screening, saying that only a "limited number" of users were affected.
The support thread dedicated to the problem, however, grew by bounds. Yesterday, it boasted more than 250 messages - double the number of 12 hours before - and had been accessed over 55,000 times.
Bryant encouraged Windows XP users to apply the security updates other patches, and to protect their machines in lieu of the now-missing MS10-015 with a automated workaround that disables the vulnerable NT Virtual DOS Mode (NTVDM) subsystem.
MS10-015 quashed a pair of 17-year-old kernel bugs in all 32-bit versions of Windows. The vulnerability went public three weeks ago when a Google engineer published proof-of-concept attack code.
Microsoft did not provide any new help to users whose machines have been incapacitated, nor did Bryant provide a timetable when the company would conclude its investigation.
The only Microsoft-endorsed solution, which was posted to the support forum Wednesday by a user, is worthless to netbook owners whose systems lack a CD or DVD drive.
However, someone identified as 'John E' and labelled as a Microsoft employee asked users with the blue screen problem to submit a memory dump file from their PCs for examination.
The impact now stretches beyond Microsoft.
Not surprisingly, rumors began circulating about possible causes of the apparent conflict between the MS10-015 update and some, though certainly not all, Windows XP machines.
One making the rounds ended up on the support thread: "Is it true that the [Blue Screen of Death] only happens on people already infected with the malware that this update is supposed to fix?"
Several users jumped in to reject that theory, a good bet since although exploit code was publicly disclosed several weeks ago, Microsoft said that it had seen no in-the-wild attacks.
This week's incident was not the first where a Microsoft update has harmed rather than helped.
Two years ago, a set of updates for Vista sent machines into an endless series of reboots . Similar problems stymied users who tried to upgrade to Windows XP Service Pack 3 (SP3) in May 2008, and others attempting to upgrade from Vista to Windows 7 last October.