All invalid hostnames resolve to localhost in my browser. What is going on?

Some ideas:

• Are you SURE this is your localhost? Or... could it be that your DNS server is also running IIS and serving that default page for domains that do not resolve? Have you tried disabling your local IIS server?
• Also blaming the DNS server, could it be that the DNS server returns 127.0.0.1 for non-existent domains?
• Have you checked the local routes to see if anything odd appears? To view, pull up a command prompt and enter "route print".

How to test whether the DNS server is misconfigured:

1. Open your local network adapter settings, and change your IPv4 and / or IPv6 DNS settings from "Obtain DNS server address automatically" to "Use the following DNS server addresses".

2. Set the Preferred and Alternate to something else, such as Google Public DNS or Neustar's DNS Advantage:

   • https://developers.google.com/speed/public-dns/
   • http://www.neustar.biz/enterprise/dns-services/free-recursive-dns

3. Try the bad domains again.

For the win: This guy's answer (seems to have gotten you to the right place): All my browsers suddenly don't support Javascript files anymore?

Congrats. Glad I could at least help steer you in the right direction :)