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Abstract. In the last years, social networking sites (SNSs) have enjoyed an undeniable success. Those web platforms have huge quantities of active users sharing lots of information everyday. Usually, user-generated content may be almost innocuous, however, some studies have shown that it may also contain very sensitive personal data. This situation may pose a serious privacy threat to the users due to the fact that third parties can gather and exploit that knowledge for their own benefit. There are some proposals in the literature that try to address this situation. Nevertheless, they fail to provide a practical solution capable of working with well-known SNSs. In this paper, we propose a new scheme that fills this gap. More specifically, we present a privacy-preserving system that enables the users to decide which individuals (e.g., other users, third parties or even the SNS itself) can access to their user profiles. We have implemented our scheme to be used by Facebook users. We have run some tests with our prototype and the results show that the added overhead is affordable.