Microsoft's update to Windows Vista's PatchGuard, a kernel protection scheme designed to keep malicious or unproven code at arm's length, has nothing to do with recent hacks of another Vista defence, Microsoft claims.

The update to Kernel Patch Protection (KPP), also known as PatchGuard, was issued on Tuesday to Vista 64-bit users, but the description of the enhancement was unclear. All Microsoft said at the time was "this update adds checks to this protection for increased resiliency in Windows".

Third-party researchers filled the vacuum with speculation about the update's purpose, with much of that speculation centring on a possible connection between the update and multiple disclosures that Vista's kernel code signing defence - another barrier Microsoft set up to protect the kernel, but separate from PatchGuard - could be easily circumvented.

When asked to describe the update's intent, Ollie Whitehouse, a Symantec researcher tracking Vista kernel signing, said he believed Microsoft was reacting to the code-signing evasions by toughening up PatchGuard. "It looks like they are trying to make it harder to do anything malicious once you've exploited vulnerabilities which allow code to be executed in the kernel, such as the ATI driver," Whitehouse said.

Microsoft claimed that wasn't the case. "These are unrelated events," said Russ Humphries, a senior product manager on the Vista team in a posting to the group's blog. "Perhaps the mix up is due to a confluence of events, or - put another way - the fact that we released an update to KPP at the same time that news about an ATI driver issue appeared," Humphries continued. "The update to KPP has no relationship to the ATI driver issue or recent topics related to code signing."

Others in the company pointed out that PatchGuard, or KPP, has been updated before. During Microsoft's monthly post-patch webcast on Wednesday, Mike Reavy, a program manager with the Microsoft Security Response Center, said: "It's normal for us to update [KPP] on an ongoing basis. This is the second type of update we've released."

For his part, Ionescu agreed that his utility and the PatchGuard update were not conjoined. "They're not related," he said. "The [PatchGuard] patch was gonna come out either way."

See also:

Windows Vista review