Security Update 2016-006 (Yosemite) and 2016-002 (El Capitan)
Apple has released Security Update 2016-006 for OS X 10.10 Yosemite and Security Update 2016-002 for 10.11 El Capitan, bringing a few select patches from the macOS 10.12.1 Sierra release to the two older operating systems (see “macOS 10.12.1 Sierra, watchOS 3.1, and tvOS 10.0.1 Mostly Fix Bugs,” 24 October 2016). For both systems, the security update addresses a couple of memory corruption issues and an SGI image parsing issue. (Free. For 10.10.5 Yosemite, 473.6 MB; for 10.11.6 El Capitan, 414.9 MB; release notes)
This update was problematic on one of my Macs.
Using App Store, I tried installing 2016-002 on an iMac with 10.11.6. It told me it had to reboot, which I approved. The iMac rebooted, then displayed a gray screen with the Apple icon and a black progress bar. Over a few minutes, the progess bar went from 0 to 100%, then stopped at 100% and stuck there for at least 5 minutes. I went away for a while to attend to another Mac. When I returned, there was nothing but a gray screen. The progress bar and icon had disappeared.
I left it with the gray screen for a half-hour. When nothing further happened, I forced it to reboot with the power switch.
After reboot and logon, I returned to the App Store. It showed No Updates available, but did not list Security Update 2016-002 under Updates Installed in last 30 days.
To ensure that this update really got installed, I downloaded it from apple.com/support and installed it manually. It still doesn't appear in the App Store's list of recent updates, but I assume it's been installed by the manual installer.
So in summary:
1) this update may not get successfully installed via the App Store.
2) App Store doesn't reliably indicate which updates have been installed.
This update caused big problems with my NVIDIA GTX 660 graphic card installed in a Mac Pro 4.1. Getting problematic crashes when converting RAW files to JPEG in Lightroom 6. This never happened before. I returned to my "old" Yosemite system and everything works fine again......