Q: How do I find information about a Security Update that I was just notified was installed if the App Store Update section does not does not have any record of a recent security update?

Here ya go.

About OS X NTP Security Update - Apple Support

If you want more control over updates, like being able to read about them beforehand and then deciding whether you want to install them, don't allow them to be installed automatically. You can change this setting in your App Store system pref.

After all the problems with the Safari update to 8.0.1 it is wise not to allow automatic updates.  Probably best to have the MAS inform you of an update and then do some research on here before installing it.

Open System Information and look through the Software>Installations section. I'm not at a Mac right now, so I don't know exactly what to look for.

@erpilgrem, the only thing I can recommend would be to reference this list after having seen the notification - Apple security updates - Apple Support

The suggestion to check system info (about this mac / system report / installations) did not work for me. The list didn't reference the most recently installed security update.

Last night after receiving a “Fly-In” message that a security update was installed on my system I contacted Apple Support.  We spent an hour and a half trying to figure where the message came from and what update was installed.  No mention of the auto update and there is no history in Apple’s files, the App Store and my version of  OS X Yosemite never changed after this update.  http://www.cnet.com/news/apple-updates-macs-without-asking-but-its-to-foil-hacke rs/#ftag=YHF65cbda0

Received same notification.

Looked in SysPref/Software/Installations and found: 12/22/14 Software Name:OSX NTP Security Update; Version: 1.0;  Source: Apple

Strange. Never noticed this happening before. It has finally happened: Big Brother is watching.

I Haven't read anything deck I've got ice e, but someone else posted here that it was a "critical" updat that installed automatically.

I'm Not aware that has happened before.

This happened to me today.

It was indeed a first for Apple.

http://www.reuters.com/article/2014/12/23/us-apple-cybersecurity-idUSKBN0K108W20 141223

In System Preferences> App Store there is a box 'install system and security updates'--if this box is checked, the updates will be installed automatically, but if left unchecked, the update appears in regular update window and must be OKd.

I have absolutely nothing checked in the App Store pane of System Preferences and, after reading about the security update yesterday, I downloaded it manually and then installed it. There was nothing automatic about it: