To make a long story short, I found that it caused the following problems:
1. I could no longer update Bracket's extensions.
2. I could not run IPython notebooks, getting the error message:
WebSocket connection failedA WebSocket connection could not be established. You will NOT be able to run code. Check your network connection or notebook server configuration.
It took me many hours, deleting my IPython profile, uninstalling and reinstalling IPython, doing the same with Tornado, trying in various browsers, searching for posts about people having had similar problems, etc., etc., etc. until I found this stackoverflow post which had a different problem but made me think that it was perhaps related to an anti-virus program issue.
I stopped MadAware (and restarted the default Windows Defender) ... no change. On a hunch, I uninstalled it and rebooted (for the Nth time) my computer.
Sure enough, that was the problem.
After deleting MadAware, my problems went away.
I had to get this off my chest before I could resume working on tomorrow's lesson where I wanted to show off the IPython notebook.