Microsoft said last week that it will put filters in place to make sure AMD-powered PCs susceptible to an "endless reboot" problem can't receive Windows XP Service Pack 3 (SP3) from the Windows Update service.

It marked the second time this month that Microsoft has had to bar some systems from obtaining the long-awaited service pack.

The move was in reaction to a weeklong debacle during which some PCs equipped with processors from Advanced Micro Devices rebooted repeatedly after being upgraded to Windows XP SP3.

According to users who diagnosed the endless reboots -- and Microsoft when it first weighed in last week -- some computer makers made the mistake of using a disk image created on an Intel-based machine to factory-install Windows XP on hardware running AMD chips. Microsoft had advised computer makers against doing that as long ago as 2004.

Users afflicted with endless reboots had fingered HP as responsible, saying that their affected PCs were HP-branded desktops. Last week, HP confirmed the snafu and said it would issue a patch.

Microsoft echoed HP in a message of its own on Thursday, but did not call out its OEM partner by name.

"We've determined this problem occurs on AMD-based machines with Windows XP images that were originally captured by an OEM on an Intel-based machine," said Microsoft in an anonymous post to its Micrososft Update team's blog. "The problem is a registry value, present on images created with Intel processors, that causes a driver (intelppm.sys) to load at boot. When intelppm.sys attempts to load on an AMD-based system upon the install of SP3, it causes a blue screen and the continuous reboot."

The same post acknowledged that engineers were working up a fix.

In the meantime, Microsoft will block AMD-based PCs which have the errant registry key from receiving XP SP3 through Windows Update (WU). "We're planning to add a filter to prevent Windows Update from offering SP3 to affected systems," the post continued.

It is not the first time this month that Microsoft has had to selectively ban some PCs from getting the service pack. In early May, the company added filters to stop machines running its retail point-of-sale software, Microsoft Dynamics Retail Management System (RMS), from downloading XP S3 after it confirmed the upgrade could corrupt and destroy RMS data.

Microsoft had postponed the availability of XP SP3 for a week while it investigated the RMS bug and crafted a WU filter. Ironically, the new endless reboot problem cropped up almost as soon as Microsoft deployed the RMS filter and released XP SP3 to general distribution through Windows Update.

Users impatient with HP's patch plans or Microsoft's filtering scheme can instead download a free tool crafted by Jesper Johansson, a former Microsoft program manager, that detects and fixes PCs susceptible to the endless reboot.