A method and apparatus for modifying a video signal to allow it to carry encoded data which is detectable at a suitably compliant receiver but is not recorded by a conventional video recorder. One application is to carry a descrambling key to prevent useful recording (but not viewing) of a scrambled television signal since the key will not be recorded. This encoded "hidden" data is not recorded by the conventional video recorders because, for instance, it is located in the vertical or horizontal blanking intervals of the video signal, or is carried by a high frequency carrier signal, or is expressed by phase modulation of the video signal's synchronization pulses.