The invention relates to a microprocessor-controlled standard field device (3', 4', 5', 6'), such as a measuring sensor or an actuator, for connecting to a field bus system (1) that, in turn, is connected to, for example, a freely programmable controller (2'). According to the invention, the field device (3', 4', 5', 6') is equipped with a security layer (10) for carrying out a security proven communication. A secure and simultaneously cost-effective communication with a control device (2) via a field bus system (1) is made possible by implementing a security layer (10) in a conventional operationally proven or redundant standard field device (3, 4, 5, 6).