Apple has released a new security update for OS X Yosemite and El Capitan, or OS X 10.10 and 10.11, the operating system released two years and one year ago. Apple hasn’t yet detailed what security fixes are included beyond these release notes:
Security Update 2017-001 is recommended for all users and improves the security of OS X.
The update could be related to recent security vulnerabilities detailed in the news or routine maintenance for older versions. macOS 10.12.4 is the latest version of the Mac operating system for compatible machines and was released earlier today.