The problem of wireless security for the downlink of multi-stream multicasting MIMO systems overheard by multiple multi-antenna eavesdroppers is investigated. We assume that the transmitter has perfect knowledge about the channel to desired users and the eavesdroppers. An efficient secure precoding scheme is devised that is based on signal-to-leakage-and-noise ratio (SLNR). The scheme maximizes the overall minimum SLNR of intended users subject to constrains on total available power and maximum allowable signal-to-interference-and noise radios (SINRs) of the eavesdroppers. Our design decouples the precoder design problem by using SLNR and advocates joint optimization of the precoding matrices and AN spatial distribution with lower computation complexity. Simulation and complexity comparison are provided to show the benefits of the proposed scheme.