I'm having this problem as well, absolutely nothing has helped me remove it whatsoever.
Moved this to Home User Assistance as the proper area for it.
There is an excellent removal guide here: Remove "Ads by DNS Unlocker" virus (Uninstall Guide)
No antivirus is guaranteed 100%, a lot depends on you, what you click on,. what strange emails you open, download stuff without checking for unwanted "optional" extras, etc. etc.
I've written some guidelines and have useful free tools listed here: Anti-Spyware/Malware/Hijacker Tools