Facebook is the privileged target for hackers and cybercriminals, the popular social network is a mine of data that could be used to acquire information on a specific target or to conduct criminal activities involving a large audience. The analysis of mutual relationship between users an attacker could elaborate the proper strategy to hit a victim, or a group of individuals. The study of friend list is another powerful practice to profile a target, but it is known that through privacy setting Facebook users can make the friend list public or private.”]
Source: http://securityaffairs.co/wordpress/19920/social-networks/facebook-flaw-friend-list.html