Users of the latest 64-bit version of Microsoft's Windows XP Professional x64 Edition operating system will not have the option to install Norton or McAfee antivirus software, vnunet.com can reveal.

Users trying to install the Norton Internet Security 2005 security suite for consumers on the 64-bit version of Windows see an error message stating that the product can not be installed.

They are referred to a web page which states: "Symantec currently does not sell any consumer products that are certified to be compatible with 64-bit processors and operating systems."

A similar error message pops up when trying to install McAfee security products.

Spokespeople for Symantec and McAfee did not respond to requests for further information in time for this story's posting.

Symantec has previously stated that it will support 64-bit Windows in its corporate antivirus product, but does not list an expected release date.

McAfee's website fails even to mention the latest version of Microsoft's operating system.

Microsoft launched 64-bit versions of its XP Professional and Server 2003 products on Monday at WinHEC in Seattle.

Users who purchased a desktop system capable of running 64-bit software with Windows XP Pro preinstalled after 31 March 2005 can request a free upgrade provided they pay for shipping costs. The offer will remain valid for future system purchases through to 31 July.

Microsoft will launch an antivirus service later this year, but in an email to vnunet.com a spokeswoman for the company declined to discuss product specifics, including support for 64-bit Windows.

She also pointed out that Windows XP Professional x64 Edition and Windows Server 2003 x64 Edition are inherently more secure than most Windows software that is currently deployed. Both use security improvements that were made available in Service Pack 1.

Rob Enderle, principal analyst with the Enderle Group, warned that it could take Symantec and McAfee between 30 and 180 days to make security software available for 64-bit Windows.

Security vendors usually have more time to release software for a new operating system, Enderle pointed out. Because retailers need time to stock systems that run the new operating system, there is a time gap between when the software is finished and the official launch.

But 64-bit Windows XP systems will not ship preinstalled with new systems, at least for now, so the antivirus software developers had less time to prepare.

The lack of protection for x64 Windows is not the only reason why consumers should put off switching. Hardware vendors have to develop new drivers for the system and there is currently only a limited number of drivers bundled with the software.

The same drivers can be used for Longhorn, the next major release of Windows that is scheduled for release late next year. By then most computers will support 64-bit.

"This [Windows XP x64] platform is more of a warm-up for Longhorn," Enderle said.