BlackBerry is the first non-Google OEM to push April security patch
Considering the update has just been made available by Google for its Nexus and Pixel devices, alongside Android 7.1.2 Nougat, it looks like a great achievement on BlackBerry's part.
Besides starting to push the update to its smartphones, BlackBerry published the Android Security Bulletin that contains all the vulnerabilities fixed in this update. Apparently, there are quite a lot of security issues that have been addressed in this patch.
source: BlackBerry via CrackBerry
Things that are NOT allowed: