Physical layer security has been recognised as a promising technique to realise secure wireless communications. A novel interference masking approach is proposed for secure broadcast scenarios. Specifically, when there is an external jamming node, precoding matrices at the source and jammer are carefully designed to ensure that each destination can detect only its own message, and not the information intended for other destinations which is masked with artificial noise. When there is no external jamming node, interference masking is implemented through user cooperation, in which destinations switch roles from jammer to relay nodes during different time slots. Both analytical and numerical results are provided to demonstrate the performance of the proposed approaches.