santosh maharshi writes "On social networks like Facebook, even if you have kept your profile very private, people can just look at your friends list and infer lots of vital information about you. Most of the social networks like Facebook and LinkedIn allow people to see your picture and your friends list as part of the open access for visitors (the article says that only 5% of Facebook users have bothered to hide their friends list). In a study titled You Are Who You Know: Inferring User Profiles in Online Social Networks (PDF), conducted by Alan Mislove of Northeastern University and his colleagues at the Max Planck Institute for Software Systems, an algorithm was tested that can accurately infer the personal attributes of Facebook users simply by looking at their friend lists. 'At Rice [University], the algorithm accurately predicted the correct dormitory, graduation year, and area of study for the many of the students. In fact, among these undergraduates, researchers found that “with as little as 20 percent of the users providing attributes we can often infer the attributes for the remaining users with over 80 percent accuracy."'"