A circuit has a first memory for modifiable storage of information, the information being modifiable by an ambient parameter of the circuit, which ambient parameter acts on the first memory. The first memory includes a test memory area for storing test information. The circuit also includes a second memory for unmodifiable storage of reference information and a detection circuit. The test information and reference information is supplied to the detection circuit. The detection circuit then detects whether a modification of the originally stored test information has been brought about by an ambient parameter acting on the first memory.