Microsoft will allow security developers access to the kernel in Vista 64:
In another change, Microsoft had planned to lock down its Vista kernel in 64-bit systems, but will now allow other security developers to have access to the kernel via an API extension, Smith said. Additionally, Microsoft will make it possible for security companies to disable certain parts of the Windows Security Center when a third-party security console is installed, the company said.
Microsoft’s attempt to lock the kernel through PatchGuard was very worrisome to the security community. It would have been a significant handicap to the security community against the battle against malware authors.