The process started in Australia and Brazil, and is to gradually roll out worldwide this year. Microsoft has declined to provide the names of countries where it has switched on the silent IE upgrades.
Apple's Safari lost two-tenths of a point last month to end at 4.6 percent, while Opera Software's Opera was flat at 1.6 percent.
StatCounter's calculations, however, were considerably different than Net Applications', as they tend to be.
Net Applications had IE falling by almost two percentage points to 32.1 percent, while Chrome grew by 1.2 percentage points to 32.4 percent, making good on reports throughout May that showed Chrome would kick IE out of first place. Firefox, said StatCounter, climbed to 25.6 percent, while Safari and Opera didn't budge, accounting for shares of 7.1 percent and 1.7 percent, respectively.
Net Applications calculates browser usage share with data obtained from more than 160 million unique visitors who browse 40,000 Web sites that the company monitors. More browser share figures can be found on the company's site.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is firstname.lastname@example.org.
Read more about browsers in Computerworld's Browsers Topic Center.