My speculation on iOS 11.3.1 show on picture.This is the moment when silence is more expressive than all words ever spoken. For more details about official announcement. Please see below url for references:
About the security content of iOS 11.3.1
About the security content of Safari 11.1
https://support.apple.com/en-us/HT208741
About the security content of Security Update 2018-001