Security Update 2015-004 Available for OS X Mavericks & Mountain Lion
Mac users who are running OS X Mavericks and OS X Mountain Lion will find an important security update available to them. Labeled as Security Update 2015-004 1.0, the software update includes many fixes to a wide variety of potential security issues for OS X, and is therefore recommended for all Mac users running OS X 10.9.5 or OS X 10.8.5 to install.
Users who are running OS X Yosemite will find the same security fixes bundled within the OS X 10.10.3 software update, thus there is no separate security update patch available for Yosemite.
To get the security update for OS X Mavericks or OS X Mountain Lion, you’ll want to run the Updates mechanism of the App Store, available through the Apple menu > Software Update. If you don’t find the update immediately available, hit Command+R to refresh the Updates tab of the Mac App Store.
The update download is fairly small but requires restarting the target Mac to complete installation of.
Even though it is a small update, it’s still good practice to start a back up with Time Machine before installing.
Those interested in learning specifics, including what aspects of kernel, apache, php, openssl, and others system functions are patched, can read more about the security update here on the Apple website.