Windows Update had the follwing update a few minutes ago
Definition Update for Windows Defender - KB915597 (Definition 18.104.22.168)
Download size: 18.3 MB
After downloading curiously fast I got an error message that installation had failed. I "tried again" but download window was not showing any progress so I cancelled, figuring I would start the process over again. However, after cancelling the window changed to the successfully installed window. The history window now says the update was successful as well.
Any idea what's going on. Not only have I not seen behavior like this before but I googled and see that others are having problems with this update.