# Privacy and Security Issues in Online Social Networks
## 1 Introduction  
Social media are a source of communication between the data owner (data generator) and viewers (end users) for online communications that create virtual communities using online social networks (OSN) [1]. A social network is a social graph that represents a relationship among users, organizations, and their social activities. These users, organizations, groups, etc., are the nodes, and the relationships between the users, organizations, groups are the edges of the graph. An OSN is an online platform used by end users to create social networks or relationships with other people that have similar views, interests, activities, and/or real-life connections [2]. A large number of different types of social-networking services are available in the current online space. The following are some of the common features in social-networking sites [2, 3]:  
* All current online social-networking services are web-based, using an Internet connection. Contents are stored on cloud storage through a centralized access management system. These contents can be accessed from anywhere using an Internet connection and web browsers. * OSN users need to create a public profile for social-network sites as per their predefined format. This profile information is primarily used for the authentication process to log into the social-networking site. * Almost all existing social-networking services facilitate users in developing their social relations with other users by connecting a user's profile with others having similar profile information. * One interesting feature of the existing OSNs is that contents on these sites are user-generated, while OSNs use these contents for business purposes. The main goal of OSNs is to share contents with maximum users. Users utilize OSNs, such as Facebook, Twitter, and LinkedIn, to publish their routine activities. Sometimes, OSN users share information about themselves and their lives with friends and colleagues. However, in these published data, some of the revealed contents through the OSN are private and therefore should not be published at all. Typically, users share some parts of their daily life routine through status updates or the sharing of photographs and videos. Currently, various OSN users utilize smartphones to take pictures and make videos for sharing through OSNs. These data can have location information and some metadata embedded in it. OSN service providers collect a range of data about their users to offer personalized services, but it could be used for commercial purposes. In addition, users' data may also be provided to third parties, which lead to privacy leakages. This information can allow malicious users to leverage and invade the privacy of an individual [4]. Information retrieval and data privacy are two growing areas in computer-science disciplines that have different goals. Information retrieval provides methods for data extraction. It also offers a set of techniques to an organization for data analysis and making decisions based on this retrieved information. Data privacy protects information from unauthorized and malicious access that discloses, modifies, attacks, or destroys the data stored or shared online. For example, researchers related to information retrieval sometimes do not consider privacy issues while designing solutions for information retrieval and management. On the other hand, researchers who work on data privacy usually restrict information-retrieval techniques to protect sensitive data from adversaries who seek personal information. With the emergence of social media and the growing popularity of online communication using OSNs, more sensitive information about individuals is available online. Though much of the data that are shared through OSNs are not sensitive, some users publish their personal information. Thus, the availability of publicly accessible sensitive data can lead to the disclosure of user privacy.