Abstract: A safety device for diagnostic terminals (3) in distributed computer networks (8) containing at least two nodes and a common communication bus (10a, 10b) for the computer network, preferably implemented in vehicles. The diagnostic terminal enables connection of an external diagnostic equipment (1) to different nodes (20a, 20b, 20c) within the computer network. By a signal evaluation circuit (12) arranged in the computer network a detection of the signal state at the contact pin or pins (3a, 3b) in the diagnostic terminal can be made, which contact pins connect the diagnostic equipment to the communication bus. A predetermined signal state will indicate an authorized connection of a diagnostic equipment (1), and only after an authorized connection will a direct connection to the communication bus (10a, 10b) be established via a relay function (13, 14a, 14b).