Both factors are responsible for producing the wildly-different numbers, said Vizaccarro, who rejected page views as susceptible to automated bots "designed to influence market share." None of the browser vendors, however, have ever been accused of trying to game the system with such bots.
Country weighting gives a more accurate estimate of browser share, said Vizaccarro. Net Applications weights its data to account for the lack of Western insight into browsing habits in nations like China, where IE is the overwhelming favorite.
"If our traffic were concentrated in one or more regions, our global data would be inappropriately affected by those regions," said Vizaccarro. "Country-level weighting removes any bias by region when you calculate a worldwide number like StatCounter has done. StatCounter's global data shows a regional bias toward the countries where Chrome is used more."
StatCounter didn't take the criticism lying down. In a long blog post Monday -- titled "An Open Letter to Roger Capriotti, Microsoft," the Irish company rebutted what Microsoft and Net Applications said were its failings.
StatCounter said page views, not unique visitors, were a more accurate measurement of browser use
"Page views is the only valid metric to look at when talking about browser usage as it directly measures how much activity (or usage) is happening on each browser," said StatCounter. "It is just plain wrong to claim that 'browser usage' is measured using unique visitors."
The company also parried the issue of weighting, saying that the CIA's data on the number of online users in each country, which Net Applications uses to modify its data, was outdated -- the most recent from the intelligence agency is 2009's -- and so doesn't take into account rapid increases in activity in Brazil and India, where Chrome is the leader.
But the biggest factor in its favor, said StatCounter, was its larger sample size: 3 million websites compared to Net Applications' 40,000, and 15 billion page views each month to Net Applications' 160 million unique visitors
StatCounter also called Microsoft's affection for Net Applications' data hypocritical, since while much of the boost IE gets in the latter's data comes from China, a considerable amount of that originates from IE6 and from machines running pirated copies of Windows.
Microsoft has been trying to kill the 11-year-old IE6 since mid-2009, and has taken a strong anti-piracy stance in China, where it acknowledges counterfeit-use rate is high.
"It seems odd to rely on China to boost your global browser usage figures ... [but] usage is usage, huh?" said StatCounter.
To show the disparity between its data and Net Applications', StatCounter highlighted a five-month stretch between December 2011 and April 2012. During that period, Net Applications tracked a rebound by IE to the tune of 2.2 percentage points, from 51.9 percent to 54.1 percent. In the same five months, Chrome fell close to three-tenths of a point, from 19.1 percent to 18.8 percent.
StatCounter, however, saw a different picture in the same timeframe: IE fell by 4.6 percentage points, from 38.7 percent to 34.1 percent, while Chrome increased by about 4 points, growing from 27.3 percent to 31.2 percent.
"We're sorry to have to break it to you [Roger Capriotti] that IE actually trended down and not up over the period December 2011 to April 2012," said StatCounter. "Don't shoot the messenger!"
Microsoft said its opinions of Net Applications' and StatCounter's data had not changed.