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This paper discusses the use of a communications network security device, called a trust system, to enhance supervisory control and data-acquisition (SCADA) security. The major goal of the trust system is to increase security with minimal impact on existing utility communication systems. A previous paper focused on the technical operation of the trust system by augmenting routers to protect User Datagram Protocol (UDP)-based traffic. This paper concentrates on placing the trust system into a broader context, creates new trust system implementations to increase its flexibility, and demonstrates the trust system using TCP traffic. Specifically, the article expands on previous work in the following ways: 1) the article summarizes major threats against SCADA systems; 2) it discusses new trust system implementations, which allow the trust system to be used with a wider array of network-enabled equipment; 3) it discusses key SCADA security issues in the literature and shows how the trust system responds to such issues; 4) the paper shows the impact of the trust system when widely prevalent TCP/IP network communication is used; and 5) finally, the paper discusses a new hypothetical scenario to illustrate the protection that a trust system provides against insider threats.