Even so, Windows' market share fall for November-December 2008 was more than twice that of any similar period in the preceding three years. During the same two months of 2007, for example, Windows lost 0.7 of a percentage point, while in 2006 and 2005, Microsoft's operating system dropped 0.45 of a percentage point and 0.51 of a percentage point, respectively.

As has been the case throughout most of the year, Windows XP accounted for the bulk of Microsoft's downturn. During December, the seven-year-old operating system lost 1.1 percentage points. 's share, on the other hand, increased slightly to finish the year just above 21%.

Net Applications' numbers can be found on the company's Web site.