My problem was that security update 007-2019 wouldn't complete the update on my Mac Mini 2012
When I was prompted to update, I downloaded via App Store and followed instructions but every time, the update process stopped about half way through, saying "can not install update" and computer restarted back to the desktop.
Here's what worked :
Downloaded the update NOT via App Store, but directly from apple US :
https://support.apple.com/kb/DL2026?locale=en_US
I switched my internet connection from ethernet via router, to WiFi, just to be sure the problems were not due to an unstable internet connection.
Double clicked the installer package, and followed the instructions
Computer restarted, began the update process (45 minutes it said at first)
now everything worked fine!
hope this can help :)