Apple has pushed an update to the data used by Gatekeeper, bringing its version number to 166, dated 13 May 2019. This isn’t bundled with the concurrent Mojave 10.14.5 update, or the Sierra and High Sierra security updates, but has to be installed separately.
Apple provides no details as to what changes this update brings, but it is normally expected to include recent revocations of security certificates used in signing software.
Note that Apple has also updated the KEXT Block version for Mojave, as part of the 10.14.5 update, bringing it to 14.5.1. That doesn’t appear to be downloadable separately.
You can check whether this update has been installed by opening System Information via About This Mac, and selecting the Installations item under Software.
A full listing of security data file versions is given by LockRattler and SystHist for El Capitan, Sierra, High Sierra and Mojave, available from their product page. If your Mac has not yet installed this update, you can force an update using LockRattler, or at the command line.
I have updated the reference pages here which are accessed directly from LockRattler 4.2 and later using its Check blog button.