An apparatus includes a communication device and an evaluation unit, wherein the communication device can be linked to a communication bus and can receive secure telegrams by way of the communication bus, and wherein a secure telegram includes user data and CRC data in each instance. In at least one embodiment, in order to improve the communication within the secure bus system, the evaluation unit can determine an error rate from received secure telegrams by way of a CRC check and if a threshold value of the error rate stored in the evaluation unit is exceeded, can effect a secure state of the apparatus.