The number of PCs running Microsoft's latest operating system, Windows 7, surged by 40 percent in the week following its release, says Net Applications.

According to the web measurement company, overall, Windows continued to lose share globally, dropping 0.23 of a percentage point during October, while Apple's Mac OS X picked up most of that loss, gaining 0.15 of a point to finish the month near 5.3 percent, its highest ever.

For the week after Microsoft launched Windows 7 on October 22, the new operating system's share averaged 2.66 percent, a jump of more than 39 percent over the 1.91 percent average for the part of October prior to its retail release.

Windows 7 's peak of 3.48 percent on Saturday, October 31, represented an even larger 82 percent increase over the average of October 1 through October 22.

For the month, Windows 7 finished with a market share of 2.15 percent, up 41 percent over the 1.52 percent for September.

The numbers from Net Applications mean that about one in every 44 personal computers was running Windows 7 last month.

But some countries boast a much higher Windows 7 share, Net Applications said.

"Upon analysis of global Windows 7 usage share, we noticed a distinct pattern," the company said.

"Russia and many Eastern European countries already have significant share of Windows 7 usage. We are sure these are all properly licensed users".

The tongue-in-cheek comment was well taken: Of the top 25 countries by Windows 7 usage, 17 are in Eastern Europe or formerly part of the USSR. Slovenia, where 7.8 percent of the computers ran Windows 7 last month, led the list, followed by Lithuania in the Number 3 spot (6.5 percent), Rumania as No 4 (6 percent) and Latvia at No. 5 (6 percent). In Russia, at Number 21, 4.2 percent of all machines used Windows 7.

Net Applications' implication - that the Windows 7 share in Eastern Europe is due to counterfeit copies - is backed up by data from a May 2009 report generated by the Business Software Alliance (BSA), an industry-backed anti-piracy organisation, and research firm IDC.

In 2008, the piracy rate in Central and Eastern Europe was the highest of all seven regions the BSA and IDC tracked.

Slovenia's piracy rate - the estimated percentage of all software in use that is not legally licensed - was 47 percent last year, more than double the rate in the US. Lithuania, Rumania, Latvia and Russia, meanwhile, had piracy rates of 54 percent, 66 percent, 56 percent and 68 percent, respectively.

However Windows 7 was acquired - legally or not - its increase was outweighed by a steeper-than-usual decline in Windows XP last month.

The eight-year-old operating system lost 0.92 percentage point in October, significantly more than the 0.64 point average loss each month during the past year, falling to 70.6 percent.

Vista rebounded from September, when it fell for the first time in more than two years. Vista's October share of 18.77 percent, however, was still off its record of 18.8 percent in August.

Windows' overall share dropped 0.23 of a percentage point to 92.5 percent. Microsoft 's OS has lost about two and a half share points in the last year.

As it has repeatedly, Mac OS X was the recipient of most of the users lost to Microsoft: Apple's operating system climbed by 0.15 of a percentage point to end October at 5.27 percent, a new record and only the second time it's finished above 5 percent since Net Applications revised its methodology in June.

Net Applications measures operating system usage by tracking the machines that surf to the 40,000 sites it monitors for clients, which results in a pool of about 160 million unique visitors per month. It weights share by the estimated size of each country's internet population.

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See also: Windows pirates blamed for high malware rates