If you ask Apple, switching on "Private Browsing" in OS X Safari should keep everything you do online free from prying eyes. Not only does "Private Browsing" mode prevent websites from tracking your behavior, it also precludes Safari from remembering what pages you've visited. In other words, "Private Browsing" should keep your search history completely, well, private.
Or so you thought.
Watching porn on OS X Safari isn’t as ‘private’ as you think