This paper presents an adaptation of the JazzEnsemble group communication system that enables it to tolerate Byzantine failures. The work emphasizes scalability and good performance in the normal case, i.e., when there are no failures, while providing strong semantics to the application. The paper presents the main concepts and protocols that enable the Byzantine tolerant version of JazzEnsemble to obtain these goals. In particular, this includes fuzzy mute and fuzzy verbose failure detectors, an efficient Byzantine vector consensus protocol, and a novel Byzantine uniform broadcast protocol, as well as modifications at each layer of the system to overcome potential Byzantine attacks. Additionally, high-level protocols only rely on the oral messages model, and thus messages need to be signed only once at a low level of the system. Finally, the paper presents an extensive performance evaluation, which demonstrates the system?s scalability and efficiency, and is used to analyze the sources of performance degradation associated with various aspects of overcoming Byzantine failures.