The enormous success and diffusion that online social networks (OSNs) are encountering nowadays is vastly apparent. Users' social interactions now occur using online social media as communication channels; personal information and activities are easily exchanged both for recreational and business purposes in order to obtain social or economic advantages. In this scenario, OSNs are considered critical applications with respect to the security of users and their resources, for their characteristics alone: the large amount of personal information they manage, big economic upturn connected to their commercial use, strict interconnection among users and resources characterizing them, as well as user attitude to easily share private data and activities with strangers. In this book, we discuss three main research topics connected to security in online social networks: (i) trust management, because trust can be intended as a measure of the perception of security (in terms of risks/benefits) that users in an OSN have with respect to other (unknown/little-known) parties; (ii) controlled information sharing, because in OSNs, where personal information is not only connected to user profiles, but spans across users' social activities and interactions, users must be provided with the possibility to directly control information flows; and (iii) identity management, because OSNs are subjected more and more to malicious attacks that, with respect to traditional ones, have the advantage of being more effective by leveraging the social network as a new medium for reaching victims. For each of these research topics, in this book we provide both theoretical concepts as well as an overview of the main solutions that commercial/non-commercial actors have proposed over the years. We also discuss some of the most promising research directions in these fields.

Online social networks and security issues -- Trust management in online social networks -- Controlled information sharing in online social networks -- Identity management in online social networks -- Conclusions and further research directions. 1. Online social networks and security issues -- 1.1 Introduction -- 1.2 Social networks -- 1.2.1 The meaning of community -- 1.2.2 From offline to online communities -- 1.3 Online social networks -- 1.3.1 Evolution of online social networks -- 1.3.2 Analysis and properties -- 1.3.3 Multiple social ties and social capital -- 1.4 Security issues in online social networks -- 1.4.1 Trust management in online social networks -- 1.4.2 Controlled information sharing in online social networks -- 1.4.3 Identity management in online social networks. 2. Trust management in online social networks -- 2.1 Introduction -- 2.2 Trust in computer science -- 2.2.1 Trust and policies -- 2.2.2 Trust and reputation systems -- 2.3 Trust in online social networks -- 2.3.1 Trust properties -- 2.3.2 Trust components -- 2.3.3 Social trust and social capital -- 2.3.4 Trust evaluation models -- 2.4 Conclusions. 3. Controlled information sharing in online social networks -- 3.1 Introduction -- 3.2 Access control in data management systems -- 3.2.1 A brief historical perspective -- 3.2.2 Access control models -- 3.3 Access control in online social networks -- 3.3.1 Relationship-based access control -- 3.3.2 Privacy settings in commercial online social networks -- 3.3.3 Existing access control approaches -- 3.4 Conclusions. 4. Identity management in online social networks -- 4.1 Introduction -- 4.2 Identity management -- 4.2.1 Digital identity -- 4.2.2 Identity management models: from identity 1.0 to identity 2.0 -- 4.3 Identity management in online social networks -- 4.3.1 Identity as self-presentation -- 4.3.2 Identity disclosure -- 4.3.3 Identity theft -- 4.4 Conclusions. 5. Conclusions and further research directions -- 5.1 Open security issues in online social networks -- 5.1.1 Trust management -- 5.1.2 Controlled information sharing -- 5.1.3 Identity management -- Bibliography -- Authors' biography.