Method for controlling the use of program signal in broadcast system, and control device

In a method for controlling the use of a program signal in a broadcast system, comprising one or more broadcasters and a number of receivers, at least a part of the receivers can be provided with a storage medium for storing program signals. The program signal comprises content signals of a first and a second type, wherein the second type of content signals is inserted in time slots in the first type of content signals. At least the first type of content signals is scrambled using control words as scrambling keys to obtain a scrambled program signal. The program signal is scrambled using control words as scrambling keys and the scrambled program signal is broadcasted together with entitlement control messages (ECM's) containing the control words in an encrypted manner using a second key. Decrypting means are provided at each receiver for retrieving the control words from the ECM's by decrypting the ECM's, wherein the control words are delivered by the decrypting means for descrambling the program signal. At least a plurality of ECM's comprises control information to control the decrypting means in such a manner that at least the time slots for second type of content signals are maintained in the first type of content signals.