Microsoft has come under fire for quietly releasing a fix to its PatchGuard kernel-protection software. PatchGuard is a much-touted security addition to Windows Vista that restricts access to the Windows kernel. Microsoft has had to be careful about permitting changes to PatchGuard, as any changes to the software could possibly become a new avenue of attack for hackers. Security researchers say Microsoft violated its own policy by releasing the hotfix to improve performance of its Virtual Server 2005 product. Microsoft disputed Johnsons characterization, saying that Microsoft revised this policy in October.”]