This morning, a list in Microsoft Defender's database of Windows Update causing havoc on people's Windows PCs.
The actual threat is only mentioned as "This generic detection for suspicious behavior is designed to catch potentially malicious files".
The good news is that your computer, if you are experiencing this problem, is not infected with any virus or malware
This detection appears to be a false positive, according to the Microsoft support forum,
Where a list in Microsoft Defender's database incorrectly reports activity as dangerous.
The common thread among users experiencing this issue is "use of Electron-based or Chromium-based applications,"
including Google Chrome, Microsoft Edge, and anything running Visual Studio Code.
The problem seems to stem from Defender definition/update version 1.373.1508.0,
Which means Microsoft needs to update that file and fix the problem.