Google on Tuesday said it will switch off Chrome security updates in under five months for about one-in-seven Windows users and around the same portion of those running Apple's OS X.
As of April 2016, Google will stop patching known Chrome vulnerabilities on 2001's Windows XP and 2007's Windows Vista. Together the two operating systems powered 14.8% of all Windows PCs last month.
The browser won't suddenly refuse to work, but fixes for security flaws, including those that may already be in a hacker's toolkit, will not be offered to Windows XP and Vista customers. Once April arrives, users running those operating systems will not be served any Chrome updates, which often include not only bug fixes but also feature and functionality changes.
Google will also axe support for three older editions of OS X, the operating system exclusive to Apple's Macs: OS X Snow Leopard, Lion and Mountain Lion. The trio, also labeled as OS X 10.6, 10.7 and 10.8, respectively, were introduced in 2009, 2011 and 2012.
Last month, Snow Leopard, Lion and Mountain Lion accounted for 14.6% of all OS X editions whose users went online, according to Web analytics company Net Applications.
"Such older platforms are missing critical security updates and have a greater potential to be infected by viruses and malware," said Marc Pawliger, the director of engineering for Chrome, in a brief post on a Google blog. "If you are still on one of these unsupported platforms, we encourage you to move to a newer operating system to ensure that you continue to receive the latest Chrome versions and features."
With the exception of Windows Vista, all the operating systems facing the Chrome support guillotine have already been abandoned by their maker. Microsoft retired Windows XP, for instance, in April 2014, while Apple put Snow Leopard, Lion and Mountain Lion out to pasture in September of 2013, 2014 and 2015, respectively. Only Windows Vista continues to receive security updates from Microsoft; it won't get the heave-ho until April 2017.
Even Microsoft's and Apple's own browsers have been largely retired for their outdated OSes. Microsoft no longer patches bugs in Internet Explorer 8 (IE8) on Windows XP, although it still updates IE9 on Windows Vista. Apple last refreshed its Safari browser on Snow Leopard in May 2012, on Lion in August 2014, and on Mountain Lion in August 2015.
Beginning in April, Google will patch and upgrade the desktop version of Chrome only on Windows 7, Windows 8, Windows 8.1, Windows 10, OS X Mavericks, OS X Yosemite and OS X El Capitan.
Chrome's desertion of Windows XP was expected -- in fact, Google had previously pegged the end of this year as the retirement timeline -- but the abandonment of Vista and the three OS X editions had not been hinted at earlier.
Google likely believed purging the still-supported Vista was a no-brainer because of its low user share, a Net Applications estimate that serves as a proxy for the portion of the world's desktop and notebook personal computers that run a specific OS. In October, Vista's user share was just 2% of all Windows-equipped machines.
Mozilla's Firefox browser supports all the operating systems that Chrome will leave in the ditch, and so will become -- assuming Mozilla doesn't mimic Google before April -- the best option for most of those left behind by Chrome.
Mozilla is typically the most cautious of the top four browser makers in pulling support. It didn't retire Firefox on Windows 2000, for example, until April 2012, more than a dozen years after its debut and nearly two years after Microsoft stopped updating the once-widely-used OS.
Chrome has been on a remarkable run since the beginning of 2015, accumulating 8.5 percentage points in user share since Jan. 1. That represented an increase of more than a third. In October, Chrome's user share stood at 31.1%, a record.
So while Google's decision to end support for the five operating systems next year may dampen growth as OS laggards move on to, say, Firefox, the impact will probably be minor because of Chrome's strong position. If the kill switch had been thrown now, not slated for April, Google's browser would face a maximum downturn of 4.5 percentage points if all Chrome users on Windows XP, Vista, and OS X Snow Leopard, Lion and Mountain Lion, suddenly deserted the browser. That's very unlikely: Those users are probably as indifferent to using an obsolete browser as they are to running an outdated OS.
Although a decline of that magnitude would be an embarrassing reverse for Google, it would not unseat Chrome from its second-place spot in the browser standings.