Just a quick heads-up for you all, as I assume this may affect many readers of this blog.
It appears Microsoft made a boo-boo with a recent Windows Defender signature file that has made the ASP.NET Development Server stop working for many folks.
In case you are unaware, the ASP.NET Development Server (aka "Cassini") is the server built into Visual Studio that runs your file-system-based web site when you debug or click "View in Browser". Windows Defender is a Microsoft utility that scans your system for spyware, adware, trojans, and the like.
Anyway, it seems that a recent Windows Defender update has mistakenly identified (and of course, dutifully hosed) the hosts file entry that is required for the Development Server to run on "localhost", as a possible attempt to hijack your system.
If you recently got a Windows Defender warning (on or around March 9) about a Win32/PossibleHostsFileHijack issue, you need to read the information contained at the following link:
The page above describes the issue in more detail, and explains how to modify the hosts file to get the ASP.NET Development Server working again.
Just tryin' to be a good citizen and all. Pass the word.