The OS X El Capitan 10.11.3 update improves the stability, compatibility, and security of your Mac. This update is recommended for all OS X El Capitan users.
This update contains bug fixes and security updates.
For more detailed information about this update, please visit:https://support.apple.com/kb/HT205356
For detailed information about the security content of this update, please visit: https://support.apple.com/kb/HT201222