While it admits it’s not possible to pin down an exact number, Microsoft has let out word today that it estimates the counterfeit rate of Vista to be about half that of XP, a figure that it seems to be more than pleased with. Of course, one could interpret those numbers in slightly less positive ways, but Microsoft claims the sharp dip in piracy is due to Vista’s amped up authentication system, which it says is a “proven and effective way to combat piracy.” To come up with the numbers, Microsoft apparently relied statistics based on Windows Genuine Advantage validation failures, as well as other unspecified internal data. As TG Daily notes, all this follows Microsoft’s announcement of revised anti-piracy measures in Vista SP1 and, specifically, some big changes to the aforementioned WGA feature.

Microsoft’s statistics are based on Windows Genuine Advantage validation failures, along with other internal data.

Microsoft’s statement on counterfeit data comes as it reveals new piracy prevention plans for Vista’s first service pack. “What is changing with SP1 is the nature of the experience for those systems that are never activated or that fail validation,” said Sievert. The service pack will also help prevent users with legitimate installs from being affected by Vista pirates.