Thank you so much!
This finally fixed my problem, and reassured me that nothing was mysteriously flawed with my security setup.
I did this:
- Windows Defender Security Center > Virus & threat protection.
- Scroll down to Ransomware Protection and click it.
- At the bottom, in the Ransomware Data Recovery section, it encouraged me to set up OneDrive.
- Next to that text was a link to Dismiss the notice. I clicked that.
This is some pretty awful user interface design for something as important as a security center. It's just wrong to hide the problem, and its resolution, in such an obscure place. In the Ransomware section, there's no indication whatsoever that this link is related to the security flag that appears in the taskbar.
The way things currently work, the Windows Defender security alert icon loses all valuefor anyone who's not signed into OneDrive, and who hadn't stumbled across this not-very-guessable link to resolve it. Since the alert is always on, it's hiding other alerts that might actually be much more pressing.