Association for Computing Machinery
User privacy has been an increasingly growing concern in Online Social Networks (OSNs). While most OSNs today provide some form of privacy controls so that their users can protect their shared content from other users, these controls are typically not sufficiently expressive and/or do not provide fine-grained protection of information. In this paper, the authors consider the introduction of a new privacy control - group messaging on Twitter, with users having fine-grained control over who can see their messages. Specifically, they demonstrate that such a privacy control can be offered to users of Twitter today without having to wait for Twitter to make changes to its system.