Apple has released Security Update 2017-001 for OS X 10.10 Yosemite and OS X 11.10 El Capitan, the two previous versions of the Mac OS prior to Sierra.

Details about the security flaws that have been blocked has not yet been published, but it is probably about the various bugs that have been discovered in recent months and has already been fixed in the Sierra, but that was not serious enough to require an immediate update of the older systems .

Both updates are available in Software Update / Mac App Store.