If you’re having problems changing your Mac’s browser’s default search engine or home page, check to see if there’s an application named Genieo in the Applications folder. This is a known troublemaker, bundled with a lot of freeware, and doesn’t do anything other than to maliciously modify your browser settings (redirecting you to sites you didn’t intend on visiting).
Unfortunately uninstalling Genieo is complicated, and the included uninstaller doesn’t work. Genieo installs both system and user launchd agents, adds itself to the System’s Privileged Helper Tools, installs a System framework, plus sometimes creates a launcher configuration file.
A good tutorial for how to remove Genieo completely can be found at http://www.macissues.com/2014/04/23/how-to-detect-and-remove-genieo-for-mac