The OS X El Capitan Security Update 2016-003 Supplemental Update fixes a kernel issue that may cause your Mac to occasionally become unresponsive.
The original version of the 2016-003 Security Update for OS X El Capitan was released on December 13 but was reissued today to include the new fix.
The update is available on Macs still running OS X El Capitan via the Software Update function in the Mac App Store and is also available as a direct download in two versions: Standard Update and Supplemental Update.
(Via MacRumors)
