Method for transmitting and receiving a multimedia content each cryptoperiod CP t of which is scrambled using a respective control word CW t, the method including: - an emitter encrypting the control word CW t using an operating key and an executable code of an encrypting algorithm that are contained in a virtual motherboard so as to obtain a cryptogram CW* t; - generating an ECM (Entitlement Control Message) incorporating the cryptogram CW* t using an executable code of a syntax constructor contained in the virtual motherboard and transmitting this ECM to a terminal; - the terminal receiving the ECM, the position of the cryptogram CW* t in the received ECM being located using an executable code of a syntax analyzer, the cryptogram then being decrypted using the operating key and an executable code of a decrypting algorithm, the executable code of the syntax analyzer and of the decrypting algorithm being contained in a virtual daughterboard associated with the virtual motherboard; and - unscrambling the cryptoperiod CP t of the scrambled multimedia content using the decrypted control word CW t, characterized in that the method also includes: - the emitter changing, at least every two hours, the virtual motherboard used to obtain the cryptogram CW* t+n, in a subsequent cryptoperiod CP t+n, of the same multimedia content, the new virtual motherboard used differing from the preceding virtual motherboard used in its operating key and at least the executable code of its encrypting algorithm or of the syntax constructor; - in response, the terminal selecting a new virtual daughterboard to be used to decrypt the cryptogram CW* t+n so as to obtain the control word CW t+n; and - selecting, depending on the multimedia content to be scrambled, a set of a plurality of different virtual motherboards from a plurality of sets of virtual motherboards, using a relationship associating, with each multimedia content, a single set of virtual motherboards, each virtual motherboard exclusively belonging to a single set, - the control words for scrambling a multimedia content being encrypted only using virtual motherboards selected from the set associated with this content, so as to limit access to the scrambled multimedia content solely to receiver terminals having a pre-recorded set of virtual daughterboards corresponding to this set of virtual motherboards. - an emitter encrypting the control word CW t using an operating key and an executable code of an encrypting algorithm that are contained in a virtual motherboard so as to obtain a cryptogram CW* t; - generating an ECM (Entitlement Control Message) incorporating the cryptogram CW* t using an executable code of a syntax constructor contained in the virtual motherboard and transmitting this ECM to a terminal; - the terminal receiving the ECM, the position of the cryptogram CW* t in the received ECM being located using an executable code of a syntax analyzer, the cryptogram then being decrypted using the operating key and an executable code of a decrypting algorithm, the executable code of the syntax analyzer and of the decrypting algorithm being contained in a virtual daughterboard associated with the virtual motherboard; and - unscrambling the cryptoperiod CP t of the scrambled multimedia content using the decrypted control word CW t, - the emitter changing, at least every two hours, the virtual motherboard used to obtain the cryptogram CW* t+n, in a subsequent cryptoperiod CP t+n, of the same multimedia content, the new virtual motherboard used differing from the preceding virtual motherboard used in its operating key and at least the executable code of its encrypting algorithm or of the syntax constructor; - in response, the terminal selecting a new virtual daughterboard to be used to decrypt the cryptogram CW* t+n so as to obtain the control word CW t+n; and - selecting, depending on the multimedia content to be scrambled, a set of a plurality of different virtual motherboards from a plurality of sets of virtual motherboards, using a relationship associating, with each multimedia content, a single set of virtual motherboards, each virtual motherboard exclusively belonging to a single set, - the control words for scrambling a multimedia content being encrypted only using virtual motherboards selected from the set associated with this content, so as to limit access to the scrambled multimedia content solely to receiver terminals having a pre-recorded set of virtual daughterboards corresponding to this set of virtual motherboards.