Microsoft has finally attempted to clear up confusion over the licensing of Windows Vista for power users who rebuild their PCs on a regular basis. But the answer from the software vendor did little to placate some customers, who are still upset about Microsoft's one-machine transfer policy for Vista.

According to Microsoft spokesman Mike Burk, Microsoft users who frequently change the hardware configuration of the system running Vista may fail Vista's new Software Protection Platform software-validation feature more than once. If they did, they would be required to purchase an additional licence or use Microsoft's support services to activate Vista on a newly configured machine.

He explained that Microsoft's product-activation process for Vista compares information from the initial validation - which includes the hardware configuration of the device - against the new configuration to transfer the licence to a new piece of hardware.

This process, an extension of Microsoft's WGA (Windows Genuine Advantage) programme designed to fight software piracy, uses an algorithm to help assess whether the software is installed on the same device, and validation of the software will fail if it detects a "substantially different hardware configuration", he said.

At that point, a customer can use the one-time reassignment of the licence they get with their purchase of Vista to transfer the licence to a new hardware configuration. However, if after a user does this, he or she "again exceeds the tolerance for updated components", Burk said. "The customer can either purchase an additional licence or seek remediation through Microsoft’s support services."

Burk said the situation is similar to what many XP power users experience today, and that Microsoft has improved the algorithm used to determine what hardware configuration changes constitute a new device.

"The bottom line is that the hardware tolerance of product activation for Windows Vista has been improved and is more flexible than that for Windows XP," Burk said. "We believe these improvements will better accommodate the needs of our PC-enthusiast customers."

Mark Smith, a Windows user who has his own business developing custom data-acquisition and analysis packages for industrial applications, disagreed with Burk's assessment.

"I have never heard of an XP user having to use Microsoft's remediation service to activate the software because they transferred to a new machine, did I miss something?" he said.

Smith said the licensing debacle and the new required WGA validation are reasons enough not to upgrade to Vista until "absolutely forced to”.

"[Vista] has nothing that creates an overriding desire to upgrade, and with WGA there is a strong disincentive," he said. "All recent computers that I've purchased came with XP, and I've had no reason or need to have Microsoft revalidate that they are genuine. To upgrade to Vista and face possible service interruptions if Microsoft incorrectly decides that a valid copy is not genuine is ridiculous, to say the least."

User concerns over Vista licensing began two weeks ago when it was disclosed that Microsoft is limiting the number of machines to which users can transfer Windows Vista licences as part of licensing changes to the Windows client OS. Consumers who buy licences separate from hardware will be able to transfer the OS licence they purchase to only one machine other than the one for which they originally bought Vista.