The multiple editions of IE and the two versions of Edge now available lost a combined 1.7 percentage points of user share in January, the largest one-month decline since October 2011.
IE and Edge -- Net Applications folds the latter's user share into an aggregate labeled "IE" -- accounted for 46.9% of all browsers used to reach the Web last month. A year ago, that number was 58.2%.
Meanwhile, Google's Chrome again gained significant user share, jumping to 35.1%, a 2.7-point increase from December. Mozilla's Firefox slumped by seven-tenths of a percentage point to 11.4, the lowest since October 2015, hinting that another major downturn may have begun for the troubled browser.
Apple's Safari was essentially flat at 4.6%, showing that on OS X as well as Windows, browsers built by an OS maker are not guaranteed success.
Computerworld has attributed the massive defections from IE to Microsoft's August 2014 announcement that users of older versions had to upgrade, in most cases, to IE11, by Jan. 12, 2016. Since the announcement, IE has lost 11.6 percentage points of user share, which represents a 20% decline.
The addition of Edge -- Windows 10's default browser -- has not helped. While about 3.1% of all users ran Edge in January, up from December's 2.8%, Edge's share of all Windows 10 devices actually slipped from 28% in December to 26% in January, signaling that even the newest OS users have adopted non-Microsoft browsers in large numbers.
By forcing customers to upgrade to a newer version of IE -- or alternately, go with Edge -- Microsoft opened the door to change. In this case, it had a disastrous impact on IE's user share as people, who were told they had to switch browsers in any case, used the opportunity to abandon Microsoft's and install rivals' -- notably Chrome.
If the 12-month trend continues, IE could be eclipsed by Chrome in Net Applications' user share estimate as soon as August.
The upgrade-or-lose-support deadline of Jan. 12 has come and gone, but by Net Applications' numbers, a substantial minority of IE users remain on an outdated version. The 17% of IE users running IE8, for example, are all on a browser that Microsoft will no longer patch; the same goes for most of the 7.3% who ran IE7 last month and for at least two-thirds of the 12.7% who have stuck with IE9. (The last will continue to receive security updates only if it's running on Windows Vista, the 2007 OS that accounted for fewer than 2% of all Windows copies in use during January.)
Using Net Applications' statistics and Microsoft's often-touted number of 1.5 billion Windows systems on the planet, Computerworld calculated that approximately 260 million Windows customers remain on an outdated edition of IE.