Unfortunately, nobody knows for certain how long Apple will continue to release security patches or XProtect updates for any given operating system.
Although Microsoft publicly announces its support timetables for Windows, and the Ubuntu Linux company Canonical does likewise, Apple has never given any official word to the public regarding how long each version of Mac OS X or iOS will continue to receive security updates, and Apple consistently ignores press inquiries about when levels of support will be dropped for its operating systems.
The good news is that most new Macs sold within the past several years can be upgraded to Yosemite.
Following is the list of Macs that can run a supported version of OS X. If your Mac is older than the ones listed, read on for suggestions on what you can do to upgrade to a supported system.
I have a Mac mini stuck at Tiger and some folks with MacBooks stuck at Snow Leopard. The following information might help.