Internet Explorer 10 (IE10) jumped into second place among Microsoft's browsers last month, pushing past IE9 through an enforced upgrade.
IE10's user share climbed from 16.5% to a record 24% of all copies of Internet Explorer in June, according to Web measurement firm Net Applications.
Among Microsoft's five supported browsers, IE10 was the second-most-used, leapfrogging the two-year-old IE9, which shed user share to end June with 20.9% of all copies of Internet Explorer. The 12-year-old IE6 was fourth with 10.9%, while 2009's IE8 remained in first with 40.4%.
IE10's climb has accelerated: June's user share increase was the largest since the browser's introduction on Windows 7 in February. As in previous months, June's jump was fueled by the automatic update from IE9 to IE10 on Windows 7 that kicked in last winter.
Windows 8's gradual if not dramatic rise in user share also contributed to IE10's increase, since that and Windows RT come with IE10: Windows 8's share grew in June by the largest amount since its October 2012 launch.
IE10's climb was mirrored by a large fall in IE9's user share; the browser that once threatened IE8's dominance plunged from 27.5% of all copies of IE to 20.9%. IE9 peaked in February 2013 at 38.8%, but unless Microsoft soon runs out of Windows 7 PCs to upgrade, the browser could be eclipsed by the still-surviving IE6 within a couple of months.
Overall, IE remained flat with approximately 56% of the user share of all browsers, implying that few if any of IE10's gains came from people switching browser brands. About 39% of all Windows users ran a non-Microsoft browser in June, slightly less than in May.
IE8 lost about seven-tenths of a percentage point in June -- the largest decrease since December 2012 -- to end with a 40.4% share of all copies of Internet Explorer. IE8 will remain the most popular of Microsoft's browsers for some time, experts have said, because as the most modern version available for Windows XP it's been made the standard in enterprises supporting heterogeneous environments with both Windows XP and Windows 7 systems.
The rapid rise in IE10's user share has been unprecedented in Microsoft's experience. It has been much more akin to the quick turnover by rivals like Chrome and Firefox, which also automatically upgrade users, than any previous edition of Internet Explorer, showing that the Redmond, Wash. developer can, if it wants, migrate large numbers of users to a newer browser.
But IE10's time as a climber will probably be short lived: Microsoft has promised to deliver IE11 for Windows 7, which will trigger a downturn in IE10's user share and corresponding rise in IE11.
Other browsers stayed in their long-inhabited positions in Net Applications' measurements, with Chrome exiting June with 17.2%, an increase of 1.4 percentage points, and Firefox dropping by 1.5 points to 19.2%. Apple's Safari and Opera Software's Opera remained flat at 5.6% and 1.6%, respectively.
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 email address is firstname.lastname@example.org.