To protect mobile agents from attacks by their execution environments, or hosts, one class of protection mechanisms uses reference states to detect modification attacks. Reference states are agent states that have been produced by non-attacking, or reference hosts.This paper examines this class of mechanisms and presents the bandwidth of the achieved protection. First, the notion of reference states is introduced. This notion allows to define a protection scheme that can be used to realize a whole class of mechanisms to protect mobile agents. To do so, after an initial analysis of already existing approaches, the abstract features of these approaches are extracted. A discussion examines the strengths and weaknesses of the general protection scheme, and a framework is presented that allows an agent programmer to choose an appropriate protection level using this scheme. An example illustrates the usage of the framework and its overhead.