Quoted from PinMonk:

Unfortunately, people don't realize how bad facebook is for them or their privacy. By just visiting a FB page, facebook scrapes info from your machine and uses it to profile you, and if a picture is posted of you on someone else's FB page, they will use image recognition to build a profile on you and connect you to others even though you don't have an account, then use and sell that information. They're a bad, bad company, and they can't die fast enough for me.