I just went through trying to get rid of this (Startpage) thinking it was hijacked as well....BUT... CCleaner browser has upgraded to Startpage as the default search engine. If I can get a screen capture I will edit this post and insert the image.
My workaround is to open my home page and listed my preference in the default search engine. Startpage still will be used in the new tab and address bar search despite having a different one listed in settings.