Today, Online Social Network (OSN) has emerged as the pervasive form of media connecting people from all over the world. Among the core functionalities associated with OSN, Instant Messaging (IM) plays a critical role in real-time communication between those virtual online communities. As the growth in IM usage continues, it has become the primary means of communication within business, education, and everyday life. Meanwhile, privacy management and data protection are issues that remain paramount to the future development of IM technology. In this work, we focus on the data protection and privacy management of group chat where multiple users simultaneously connect to a central server for real-time communications. We describe a novel multimedia IM system supporting user defined security control over real-time communication in a multiuser environment. The attribute-based encryption (ABE) is employed by the system to provide access control over transmitted user messages. Extensive experiments demonstrate that the new ABE key management mechanism provides a flexible and effective solution to data protection and privacy management for real-time online communication in multiuser environments.