These are adware and not really something that an anti-virus specialises in there are a number of anti-adware/spyware programs that are better at protecting from this adware/browser hijacking of your startpage.
If you haven’t already got this software (freeware), download, install, update and run it.
Note: This is a complete installer that installs HijackThis to your computer at C:\Program Files\HijackThis, making an entry in the start menu and also providing a desktop shortcut. If HijackThis is used from a temp folder, it is in danger of being accidentally deleted by clean up tools.
At the download prompt, choose “Save”. After the download is complete, navigate to the C:\Program Files\HijackThis folder and double-click it to complete the installation.