https://www.theregister.co.uk/2017/10/06/researchers_say_windows_10_patches_punch_holes_in_older_versions/

Microsoft is silently patching security bugs in Windows 10, and not immediately rolling out the same updates to Windows 7 and 8, potentially leaving hundreds of millions of computers at risk of attack.

Flaws and other programming blunders that are exploitable by hackers and malware are being quietly cleaned up and fixed in the big Windows 10 releases – such as the Anniversary Update and the Creator's Update. But this vital repair work is only slowly, if at all, filtering back down to Windows 7 and Windows 8 in the form of monthly software updates.