A clean re-installation of your OS would likely clear it but it seems like a lot of trouble for a virus that is just screwing with your DNS or Host file.

Sounds like you really just need a good anti-virus program. There is even the chance you purged the bug when you cleared your cache/s and all you need to do is repair the damage.

If and when you get the system clean you might consider installing something like Spybot Search & destroy and allow it to lock your host file and system settings.