Abstract: A security system to defeat eavesdropping in a broadcast environment has at least one transmitter and at least one receiver. The transmitter includes a transmitter memory for storing a plurality of signals in a given sequence and a marker for identifying in the transmitter memory particular ones of the signals as invalid, as well as a broadcast-transmitter for transmitting in sequence at least a portion of those signals of the transmitter memory not identified as invalid. The receiver includes a receiver memory for storing a plurality of signals in a given sequence, and a marker for identifying in the receiver memory particular ones of the signals as invalid, as well as a broadcast-receiver for receiving signals transmitted by the transmitter.