Thank you for your answer, but
The environment is Windows 7, and Windows server 2008 R2 and Windows Server 2016
All clients with no exception have the same popup since the upgrade of SCCM from 1610 to 1710
Sorry Mate, it is from SCCM as during the display of it a process in task manager appears to be running scnotification.exe, plus Windows updates are disabled across the board and only permitted Via SCCM.
So the final conclusion is, this is from SCCM.
let us assume that it is not from SCCM, keeping in mind that Direct Windows updates from the internet is disabled in the environment, and no configurations in GPO's or others to deploy from WSUS, so what is its source, and how to control it ???????