Apple has issued a security update to OS X 10.11.6 to fix a kernel issue.
Apple has released a supplemental security update for OS X El Capitan. Security Update 2016-003 can be found by heading to the Updates tab in the Mac App Store on a machine running OS X 10.11.6.
This update is meant to fix a kernel issue that could cause your Mac to become unresponsive. You'll be able to find more information on this update's security improvements once Apple updates is security support site.