The invention concerns a method for controlling access to encrypted data by control words (CW), said control words being received by a security module in control messages (ECM) and returned to a unit operating on (STB) the encrypted data. The method includes the following steps: receiving a first control message (ECM) comprising at least one control word (CW) and a time stamp (TS), receiving a second control message (ECM2) consecutive to the first control message (ECM1), said second message comprising at least one control word (CW) and a time stamp (TS), determining a duration corresponding to the difference between the time stamps (TS) of the two consecutive control messages (ECM1, ECM2), if said duration is less than a predefined duration (CP), incrementing an error counter (CE), and if said duration is not less than said predefined duration, decrementing said error counter (CE), returning the control word (CW) to the operating unit (STB) after a waiting time depending on the value of the error counter (CE).