Microsoft sold nearly 10 copies of Windows 7 every second over the last month, according to numbers the company released on Thursday. Yesterday, Peter Klein, Microsoft's chief financial officer, told Wall Street analysts of the latest Windows 7 milestone. "With 175 million licences sold to date, it is the fastest selling operating system ever, and now runs on over 15 per cent of all PCs worldwide," Klein said during an afternoon earnings call.

A month ago, Microsoft announced that it had sold 150 million Windows 7 licenses. By Microsoft's numbers, the company sold 25 million licences during the 29 days between June 23 and July 21, a pace that represents sales of 9.97 copies of Windows 7 per second.

On Tuesday, Microsoft credited strong sales of Windows 7, as well as the introduction of Office 2010, for pushing its second quarter revenues to a record $16 billion, a 22 per cent jump over the same quarter in 2009. Windows revenue grew by more than $1 billion, to $4.55 billion, according to the company.

As it has several times in the past, yesterday Microsoft called Windows 7 "the fastest-selling operating system ever." The OS has certainly outperformed its predecessor, Windows Vista.

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According to data from Net Applications, which tracks operating system usage share by monitoring 40,000 sites that use its web metrics service, Windows 7 held a 14.4 per cent share as of July 21, nine months after its release. Vista took 22 months to reach the same mark.

Klein's statement that Windows 7 now accounts for 15 per cent of the in-use operating systems worldwide not only differed from Net Applications' numbers, but also from those of Irish analytics firm StatCounter, which pegs Windows 7's current global share at 17.6 per cent. It was also muddied by a competing claim by Microsoft spokesman Brandon LeBlanc, who said that the new OS now powers 16 per cent of all PCs.

On Friday, Microsoft said that Klein had misspoke, and that 16 per cent was the accurate number. A company spokeswoman said that Windows 7's usage share was derived from internal data.