A method to identify the origin of a security module in a pay-tv system comprising: receiving by the pay-tv decoder system at least a first stream, a second stream and a control word stream, the first and second streams being encrypted by a first and a second control word, respectively, extracting from the control word stream, entitlement messages containing a main control word allowing retrieval of the first and second control words and access conditions, transferring the control word stream to the security module and checking the access conditions, selecting a current control word from the first or second control word based on part of the internal parameter, transmitting the current control word to the pay-tv decoder, selecting a current stream from the first or second stream in accordance with the selection of the first or second control word, and decrypting the current stream with the current control word.