How to check OS X installed security updates

Question

Triggered by the apple security update notification on Security update 2015-006 I updated all of the updates in the App Store (no new updates left). I was actual wondering how to check if the latest security patches were installed. No idea how to do it via GUI so tried the shell:

$ sudo cat /Library/Receipts/InstallHistory.plist | grep 2015-006

No output/hits!

So 2 questions: -How to definitely check this kind of patch level? -If concluded Security patch 2015-006 is not installed, how to install it?

Current OS version: 10.10.5

Answer 1

The list of installed security updates can also be found in the System Information app, under Software->Installations. You may want to sort by name and scroll to the S or sort by date and scroll to the most recent. The list cannot be filtered or searched.

Answer 2

If you're on 10.10.5 the 2015-006 security update is not relevant, or more precisely, is already included.
It's for users still on 10.10.4 or below, down as far as Mavericks, I think.

"Available for: OS X Mavericks v10.9.5, OS X Yosemite v10.10 to v10.10.4"

https://support.apple.com/en-gb/HT205031 has the details of what was included in the update.