Microsoft's latest security update has crippled a number of Windows XP PCs with the notorious Blue Screen of Death (BSOD).
Complaints have flooded the company's support forum.
"I updated 11 Windows XP updates today and restarted my PC like it asked me to," said a user identified as 'tansenroy' who kicked off a growing support thread.
"From then on, Windows cannot restart again! It is stopping at the blue screen with the following message: 'A problem has been detected and Windows has been shutdown to prevent damage to your computer.'"
Others joined in with similar reports. "There is something seriously wrong with the update. I can't even open in safe mode," said 'Ghellow', referring to Windows diagnostic mode that's often a last-chance way to boot a PC.
"I am not very happy with Microsoft as I got to work this morning to find my helpdesk flooded with messages that the PC has the famous Blue Screen," said 'brawfab'.
"I had to go to work and use my Mac to get online to find out what is going on with the XP updates last night," complained 'moosewalk' on the same thread.
"I am this much closer to switching over to a Mac for good."
The support thread, which was first noticed by security blogger Brian Krebs, contained more than 120 messages as of early Thursday, making it the third-longest on the Windows Update support forum. The thread had been viewed more than 2,800 times since its inception.
Several users posted solutions, but the one laid out by 'maxyimus' was marked by a Microsoft support engineer as the way out of the perpetual blue screens.
To regain control of their PCs, users were told to boot from their Windows XP installation disc, launch the Recovery Console and enter a series of commands.
Unfortunately, that left netbook users out of luck, since most of the lightweight, inexpensive laptops lack an optical drive, and so can't boot from an XP installation disc.
"Are there any fixes for netbooks, or am I essentially screwed for the time being?" asked 'HimDen'.
Several users tentatively identified the MS10-015 update as the one which triggered the BSOD, and claimed that uninstalling that security fix - which was labelled as KB977165 - returned their PC to working condition.
MS10-015, one of 13 security updates Microsoft issued Tuesday, patched a 17-year-old kernel bug in all 32-bit versions of Windows.
The vulnerability went public three weeks ago when a Google engineer disclosed the bug and posted proof-of-concept attack code.
This was not the first time that a Microsoft update has incapacitated Windows PCs. Two years ago, a set of updates for Vista sent an unknown number of 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.
Microsoft was not immediately available for comment.