—Current industrial automation systems are virtually unprotected against attacks on IT security at field level, especially if an attacker is able to connect physically to field buses or field devices. Due to resource limitations, existing protective mechanisms can not be deployed to the embedded systems of which the field level is composed. In this contribution, threats against distributed embedded systems at field level are depicted and a concept to protect the field level against such threats is deduced. The concept comprises of several protection functionalities and the mechanisms that are necessary to generate these functionalities. The mechanisms are aligned in a hierarchical structure, which provides security by cooperation of these mechanisms and enables a high degree of adaptability. Additionally, a component-based way to realize the concept is described, which allows for resource-saving implementation, in spite of high software quality and flexibility.