With the dramatically increasing participation in online social networks, huge amount of private information becomes available on such sites. It is critical to preserve users' privacy, without preventing them from socialization and information sharing. Unfortunately, existing approaches fall short meeting such requirements.
We argue that the key component of privacy protection in social networks is protecting (sensitive) content, i.e. privacy as having the ability to control dissemination of information. We follow the concepts of private information boundaries and restricted access and limited control to introduce a social circle}model. We articulate the formal constructs of this model, and enumerate the desired properties for privacy protection in the model. We show that the social circle model is efficient yet practical, which provides certain level of privacy protection capabilities to social network users, while still facilitates socialization. We then utilize this model to analyze the most popular social network platforms on the Internet (Facebook, Google+, VK, WeChat, Sina Weibo, etc), and demonstrate the potential privacy vulnerabilities in some social networks. Finally, we discuss the implications of the analysis, and possible future directions.
