The concern in our society for "cyber attacks" is increasing and cyber security has become a hot topic when it comes to protecting nation's critical infrastructures. A new technological landscape has not only made the SCADA-systems more open but also more vulnerable to cyber attacks due to existing vulnerabilities. An effective state of the art approach for understanding weaknesses of SCADA-systems is to create graphical models over the system architecture, and perform analyses based on this. Based on practical assessments, literature and interviews surveys with both industry professionals and academics this paper highlights some common pitfalls when using graphical models commonly used as a basis for cyber security assessments of SCADA- systems. (4 pages)