A method for detecting unauthorized eavesdropping. A first subscriber determines a transit time for the transmission of data to a second subscriber, adds the random value to the transit time to obtain a waiting time, waits for the waiting time, creates a data packet containing a time stamp and transmits this data packet to the second subscriber. The second subscriber records the time it receives the data packet and compares it with the time stamp contained in the data packet, determines that the data packet has arrived either: before the time indicated in the time stamp, more than a predefined tolerance time after the time indicated in the time stamp, or before or more than a predefined tolerance time after a time at which it can be expected in the second subscriber as an indication that communication between the first subscriber and the second subscriber is being eavesdropped on.