Microsoft responded this week to criticism by several security firms that the forthcoming PatchGuard functionality, which limits access to the 64-bit Vista kernel by malicious as well as legitimate code, is an anti-competitive move.

Security firms McAfee and Symantec, the owner of SecurityFocus, have both ramped up their criticism of Microsoft in the past two weeks. In July, security firm Agnitum made similar criticisms in a report on the coming Vista technology. The companies' products patch the Windows kernel to some extent to enforce their own security model on Window XP systems, but that same software mechanism will not be able to be used in the future.

Microsoft has strongly defended the move, saying that its own security products will also have to abide by the restrictions on kernel patching. The company has steadily improved the overall security of its operating system and a number of new features will debut in Vista, which is due out in January. Microsoft has also gained some support from other antivirus vendors, which have stated that they will not need to use kernel patching to protect future Windows operating systems.

Tensions between Microsoft and the top two antivirus firms, which historically have been partners on improving Windows security, rose significantly after the release of Microsoft's own antivirus and consumer security solution, Windows OneCare. Both Symantec and McAfee are preparing to release online services similar to the software giant's offering.