Something is changing my hosts file without asking

Use Process Monitor with a filter to watch the hosts file. Run it long enough and you will see everything that changes the file.

http://technet.microsoft.com/en-us/sysinternals/bb896645

I faced similar problems. I solved it by following these steps

1. Right click on hosts file go to properties.
2. Go to the Security tab.
3. Under Groups and users go to the System and edit permissions.
4. Deny write permissions for the System.
5. Press OK and Done.