This invention concerns a security module deactivation and reactivation method particularly intended for access control of conditional access data. These security modules include a plurality of registers (R1, R2, R3, Rn) containing values. The method includes the step of sending at least one management message (RUN-EMM) containing an executable code, this executable code being loaded into a memory of the security module and then executed. The execution of this code in particular can carry out the combination and/or the enciphering of the values of the registers, or render these values illegible.This method also allows the reactivation of the security modules that have been deactivated previously. In this case, the method includes the step of sending another message containing an executable code (RUN-EMM−1) for the reactivation of the modules, this executable code having an inverted function to that of the executable code used for the deactivation of the security modules.