Google will pull the plug for Chrome running on OS X 10.5, aka Leopard, after it releases version 21, which is currently in beta and will reach the browser's "stable" channel sometime next month, the company has announced.
Chrome 22, the browser that just landed in the "dev" channel -- Google maintains three primary builds for its browser, with the dev line the roughest-edged -- will not run on OS X 10.5.
"Google Chrome on Mac OS X 10.5 (Leopard) will stop receiving any updates following Chrome 21," Google said on its support site. "This includes new features, security fixes and stability updates."
Leopard was launched by Apple in October 2007, and according to Web measurement firm Net Applications, accounted for 11.6% of all versions of Apple's OS-powered machines that went online in June.
OS X 10.6, or Snow Leopard, and 10.7, better known as Lion, have a combined share of 84.4%, Net Applications said earlier this month.
Chrome 21 -- the last for Leopard -- should reach the stable channel somewhere between Aug. 7 and August 21; Chrome 22, the first that will not work on OS X 10.5, six to eight weeks after that, or in the stretch between Sept. 18 and Oct. 16. Google upgrades Chrome every six to eight weeks.
Google said the ditching of Leopard was triggered by a desire to keep users safe on the Web.
"[Leopard] is an OS X version ... no longer being updated by Apple," said the company. "While we understand this is an inconvenience, we are making this change to ensure we can continue to deliver a safe, secure, and stable Chrome for the most Mac users possible."
Chrome 21 on Leopard will not suddenly cease to work -- even after Google releases the next version, Chrome 21 will continue to run -- but it will not receive the usual automatic security fixes or be upgraded.
Apple has not patched security vulnerabilities in Leopard since November 2011, and its last security update, in May 2012, did not patch any vulnerabilities. Instead, it simply disabled older copies of Adobe's Flash Player, one of the moves Apple made to stymie the spread of the Flashback malware that infected hundreds of thousands of Macs last spring.
Nor has Apple maintained Safari on Leopard: The last update for Leopard's bundled browser was issued in July 2011.
When Mountain Lion launches later this month, Apple will probably stop serving general security updates for 2009's Snow Leopard.
If Apple hews to its decades-long habit, it will also halt Safari updates for Leopard either immediately before Mountain Lion ships or soon afterward.
Users unsure of which edition of OS X they're running should select "About This Mac" from the Apple menu at the far left of the menu bar. If "Version" reads anything other than "10.6.x," "10.7.x" or "10.8.x," it will not run Chrome 22.
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.