Microsoft's Internet Explorer (IE) browser gained more market share last month than at any time in the last three years, but at least part of the boost came from an accounting change by Web metrics firm Net Applications.
Meanwhile, Microsoft argued that its share should be calculated only as a percentage of the browsers run on Windows.
According to Aliso Viejo, Calif.-based Net Applications, IE's usage share rose by nearly eight-tenths of a percentage point to finish February at 56.8%. It was first time IE climbed since July 2010, and was the largest one-month increase since Net Applications started tracking Microsoft's browser.
But Net Applications attributed part of the increase to a change in how it weights browser data.
Like most Web measurement firms, Net Applications has more data on some countries -- the U.S., for instance -- but relatively small samples from others, such as China. So to produce what it believes is a more accurate representation of browser usage, Net Applications weights its Chinese data proportionally higher because that country has an greater percentage of the world's Internet users than the U.S.
Starting with February's numbers, Net Applications used revised online population numbers provided by the U.S. Central Intelligence Agency (CIA) that showed a large increase in the global percentage of Chinese users, with a corresponding drop in the worldwide percentage of users from the U.S., the U.K, Canada, France, Germany and other developed countries.
"This shows that China is far more influential in browser usage than anyone realizes," said Vince Vizzaccaro, vice president of marketing for Net Applications.
Using the revised CIA Internet population data caused IE's share to jump because the vast bulk of that nation's users run Microsoft's browser, not a rival like Mozilla's Firefox or Google's Chrome.
According to Vizzaccaro, the new numbers "correct an increasing inaccuracy over time as population shifts occur and reflects reality more closely than unadjusted numbers."
The result? IE jumped, and Firefox fell.
Firefox's share of the global browser market dropped by a full point, it's largest change in nearly two years, to end February at 21.7%, a mark equivalent to its December 2008 share.
"If you look at Firefox, for example, it's very dominant in Europe," said Vizzaccaro. "But it loses global share since many of the countries in Western European now have a lower percentage of global internet users."
Google's Chrome and Apple's Safari still posted gains even with the new CIA data applied, although their increases were smaller than the average of the preceding three months.
Chrome climbed by two-tenths of a percentage point -- off the seven-tenths of a point average between November 2010 and January 2011 -- to close the month at 10.9%, a new record for the browser. Safari gained a statistically-insignificant six-hundredths of a point, less than a fifth of its three-month average, to end February at 6.4%.
But while Vizzaccaro said he couldn't define the accounting change's impact -- Net Applications did not run the numbers using the old weighting scale -- he wasn't ready to credit all of IE's jump to the new CIA numbers.
"IE8 and IE9 both increased, and I don't think you can attribute those gains to China," said Vizzaccaro today. "In China, IE6 remains the dominate browser."
According to Net Applications, IE8 picked up seven-tenths of a percentage point, on par with the November-January average, to grab 35% of the browser usage share. IE9, meanwhile, edged up slightly more than its three-month average to end with a 0.6% share.
IE7 and IE6 usage both dropped during February, but at amounts less than usual. The nearly 10-year-old IE6, for instance, fell just one-tenth of a point last month using the new CIA data; in the preceding three months, it averaged a drop of 1.1 points each month.
The relatively small decline by IE6 seemed to back up Vizzaccaro's point that the browser is preferred in China.
In a blog post, Roger Capriotti, the director of IE's product marketing, acknowledged that the weighting change played a part in IE's climb.
He also defended what he said were clear gains by IE on Windows, the only platform on which IE runs.
"When adjusted using the older weighting, IE8 and 9 actually show even stronger growth on Windows: up 1.31 [percentage points] (versus 1.13 [points] using the new February weighting), or over three times Chrome's 0.42 [point] growth [on Windows]," said Capriotti. "We continue to measure our share progress relative to our addressable base, and in this case our addressable base is Windows."
Unlike Firefox, Chrome, Safari and Opera, IE only runs on Windows; all the others also run on Mac OS X, while Firefox, Chrome and Opera also have Linux editions.
Net Applications calculates browser usage share from data acquired from the 160 million unique visitors who browse approximately 40,000 Web sites it monitors for clients. The company's February browser data is available on its site.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.