televisions 2 way?

I heard a theory about how the government can "spy" on us by using cable television. somehow, according to the theory, the cable is a 2-way transmitter, and the television, when turned on, can act like a video camera for the government. I do not know ANY of the specifics of this theory, and really find it hard to believe (perhaps because I do not have any more information)...does anyone have any information on this? is this an appropriate inquiry for the cypherpunks mailing? thanks a lot sean