Important Note (from the author, who is the "I" who is speaking below):
The HOSTS file contains a change in the prefix mechanism used in the HOSTS entries, to "0.0.0.0" instead of the usual "127.0.0.1".
This was done to resolve a slowdown issue with the new Win8.1/IE11 and the HOSTS file.
I'm not sure what Microsoft changed in the new version, although I suspect it has something to do with the new "TCP loopback interface" in Win8.1 ... this change in the prefix should not affect users.
I've had some feedback from COMODO antivirus, Homer Webserver and System Mechanic, which seem to have issues with the "0.0.0.0" prefix ... to resolve this issue: You can use the "Replace" function in Notepad to convert the entries back.