Google's Chrome browser no longer runs on Windows XP, Windows Vista and older versions of Mac OS X. For users of these operating systems it's no longer possible to install or update Chrome since version 50.
Support for Mac OS X 10.6, 10.7 and 10.8 has been dropped and just like on XP and Vista the browser shows a notification that the browser is no longer supported on the operating system. In April, last year, Google already announced that it would no longer support XP, Vista and the mentioned Mac OS X versions.
Google argues that the unsupported operating systems have a bigger risk of being infected with malware.
