I recently had one changed my DNS settings.. Use HIJACKTHIS to check your DNS settings in the registry and if there you'll have to manually search/delete.. If they re-appear then a program like malwarebytes or S&D will sort out the problem, with me it was a little EXE being called from the task scheduler..
if nothing then you might want to do a scan anyway using the programs mentioned above and if nothing found then it could be someone as simple as update programs running
