Microsoft has declined to confirm statistics from its chief operating officer on the number of copies of Windows Vista it has sold, throwing into confusion how successful the operating system has been.
Kevin Turner told financial analysts on Thursday that "60 million units have been sold of Windows Vista into the marketplace".
But, approached by ZDNet.co.uk for confirmation, Microsoft could only confirm that it had sold 40 million, saying the last figure is two months old.
If Microsoft's figures are to be believed, this means Vista sales are flat. Turner's figures mean that 20 million copies of Vista have been sold, on a wholesale basis at least, over the last two months, with 40 million sold in the first four months since the consumer launch in January.
But, despite the uncertainty, Turner seized the opportunity for a spot of publicity. "By our maths, we eclipse the entire installed base of Apple in the first five weeks that this product shipped," he said.
A Microsoft spokesperson added: "Windows Vista is on track to be the fastest-selling operating system in Microsoft's history. IDC says that, for every dollar of Microsoft revenue from Windows Vista in 2008, the ecosystem beyond Microsoft will reap approximately $22 [£11]".
UPDATE: Following publication of this article, Microsoft contacted ZDNet.co.uk accepting the sales figure of 60 million licences. Its statement said: "We think demand for Windows Vista is healthy, as demonstrated by the results of our most recent quarter and the news from FAM that we've sold approximately 60 million licences of Windows Vista."