An integrated security circuit, for example, a microcontroller for smart cards, includes a function unit executing a security function. A control device determines the number of executions of the security function per unit of time. The continued execution of the security function is blocked when a threshold value is exceeded. For such a purpose, an analog timekeeper incorporating a charge storage device is preferably provided that measures the elapsing time even with the supply potential disconnected. A usage counter is updated whenever the security function is called. The security circuit offers increased protection against statistical attacks. The complexity involved in the implementation is justifiably low. The security circuit is compatible with the existing system.