Abstract: The invention relates to integrated circuits and, notably, to circuits for which it is desired to provide security against any fraudulent usage. The circuits concerned are microprocessor circuits having a program memory, a programmable non-volatile memory, at least one input/output port and an RS register memorizing the signals from sensors of abnormal conditions. This register is accessible by the microprocessor. There is provision for means to check the state of the register immediately before any operation for the writing or erasure of the programmable memory, and immediately before any transmission of data towards the exterior of the input/output port, and means to interrupt the working of the microprocessor if the check reveals abnormal conditions.