In this thesis I will show why the traditional disjoint treatment of security and fault tolerance has weaknesses if the attacker gains access to the fault tolerant system and how an integrated approach that utilizes existing fault tolerance techniques can provide security effectively. An efficient integrated safety and security approach is presented for fault tolerant systems (fail safe and fail operational), which achieves protection against attacks over the network by forming a logically isolated (sub-) network which is resilient against a bug in a software component. Isolation is obtained by diverse design of a general reusable component that prevents any unauthorized message transfer towards the secured application program. Messages from other compromised nodes are tolerated utilizing existing mechanims. The reuse of the existing fault tolerance techniques and the reuse of the additional parts needed for attacker tolerance can significantly reduce the required effort compared to existing systems.