Did Windows Defender break ASP.NET Development Server?

I was maintaining a ASP.NET application late yesterday and made good progress down my to-do list.  My eyes were getting tired, so I decided to bump up the fonts in the IDE.  I'd never done this in Visual Studio so it took me a few minutes to find the right place to make changes.  In the process I discovered a ton of other options and probably spent 1/2 an hour just looking through all the things I could customize.  Eventually I went back to work and was ready to test the site.    I pressed F5 and the dev-web-server fired up like always but then... nothing.  Empty browser.  

The app built just fine, I hadn't made any changes to any of the config files and the last round of untested code changes were minor.  I couldn't imagine how, but I figured I must have done something in some option somewhere that hosed me up.  I looked at everything and set it back - even the fonts.  No go.  I decided that I got myself into trouble because it was too late so I called it a night.

The break of dawn didn't help.  I searched all over the Internet and tried a dozen things including completely uninstalling and reinstalling Visual Studio since at least one other person solved a similar problem this way.

I must confess that I did see the solution earlier in the day, but couldn't imagine it was the solution so I ignored it.

This evening I saw that same solution again on Experts Exchange.  It caught my attention this time because the thread was from today and referenced some of the same windows updates that I had noticed.  

Windows Defender installed an update yesterday that appears to have caused this problem.  Even after disabling Windows Defender the web server would not work.

In the end it was as simple as firing up notepad (as administrator) and editing the hosts file.  (C:\Windows\System32\drivers\etc\hosts)

Mine was vanilla as installed by Microsoft when I installed Vista last summer.  There was only one line in it:

::1 localhost

This line is apparently for IPv6 and hasn't caused any trouble in over 6 months.  Based on the Experts Exchange recommendation (which matched one I saw earlier)  I changed it to the standard 

127.0.0.1 localhost

and just like that all is good in my world again.  

Thanks, Microsoft!  I'm almost back where I was 24 hours ago.  ;-)

(In hindsight, I really should have tried the System Restore I was considering last night.  What on earth was I thinking.)