After trying many of the suggestions above, this finally worked for me:
a (more generic) mod to the MS forum answer](https://answers.microsoft.com/en-us/windows/forum/windows_10-update/your-device-is-at-risk-because-its-out-of-date-and/8be130eb-493a-4f03-b655-2a4a5de42cfe?auth=1) from user [R. Anthony (Thanks, Anthony!):
**1.**Search the Microsoft®Update Catalog for latest available updates for your OS version, e.g. search "windows 10 version 1709 for x64"
Download the latest updates including the latest available CUMULATIVE update (just in case) - e.g.
2018-11 Cumulative Update for Windows 10 Version 1709 for x64-based Systems (KB4467681)
2018-12 Update for Windows 10 Version 1709 for x64-based Systems (KB4477136)
2018-12 Update for Windows 10 Version 1709 for x64-based Systems (KB4483530)
Save those in a SEPARATE folder (e.g. WinUpdTemp)
2. Open Control Panel → Programs and Features → View Installed Updates
→ Search for the KB for the latest cumulative update (e.g. KB4467681) - s/b under "Quality Updates"
→ if it is there (ie. "Successfully installed", NOT "Failed"), uninstall it
**3.**Reboot
*NOTE* after the reboot DO NOT go check for updates again, as the machine will realize KBxxx is not there and put it right back.
4. Go to the folder (e.g. WinUpdTemp) created in step 1. above and click on the latest KBxxx cumulative update and install. → re-boot as prompted.
5. Repeat the manual installation for any additional updates newer than the last available cumulative update, and re-boot if prompted.
6. Only after the final reboot check for updates.
Your error should be gone.