Microsoft put restrictions in place for all its supported operating system versions that required a special registry key be implemented and enabled to ensure that security updates would be available and installable.
This month, Microsoft has now lifted that restriction for Windows 10 devices:
Our recent work with our anti-virus (AV) partners on compatibility with Windows updates has now reached a sustained level of broad ecosystem compatibility. Based on our analysis of available data, we are now lifting the AV compatibility check for the March 2018 Windows security updates for supported Windows 10 devices via Windows Update. We continue to require that AV software is compatible and in cases where there are known issues of AV driver compatibility, we will block those devices from updates to avoid any issues.
Full guidance: Important: Windows security updates and antivirus software
Note that this is ONLY for Windows 10. Earlier operating system versions still require the registry key to be configured to continue to receive updates.
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