Facebook, since its mistakes with the Beacon advertising incident, has rolled out one of the most robust security systems for any social network, which allows users to control who sees what information about them with great specificity. Take a look at Facebook's privacy features and how to set yours.
Who Sees Your Profile
The "Basic" profile drop-down menu has four categories: My Networks and Friends, Friends of Friends, Only Friends, and Customize. A Network in Facebook is a group of people with a common interest (a city, university or workplace). So if you select "Networks and Friends" from the pull down menu, all the people in those networks you belong to can see your profile. "Friends of Friends" allows someone who is friends with your friends to see your profile. "Only Friends" gives just your friends profile access