A tool and methodology are described that can evaluate the trustworthiness of a system. In one embodiment, the system is classified in terms of the resources that constitute the system, the codes that apply to the system, the services produced by the system, the risks incurred by the system, and the costs associated with its use. A functional component of a trust decision to use the system involves a calculus to evaluate whether the probability that the services as a result of using the system will exceed the risks that may occur as valued by a user. The cost component of a trust decision includes an evaluation that the use of a system will occur at an acceptable cost and will produce economically acceptable results.