This paper discusses a technique which enables the assessment of key parameter of various intentional electromagnetic environments (IEME) for electronic systems, including the likelihood of their occurrence. The technique starts with a categorization of aspects, including non-technical aspects like availability of components, required knowledge and costs. Based on this categorization the likelihood that an offender has access to such an IEMI source is determined by a heuristic approach. In a second assessment step the possibility that a considered IEMI source might occur in the ambient of a given target system is estimated.