84 Copyright © 2015, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 5 DOI: 10.4018/978-1-4666-8456-0.ch005 ABSTRACT This chapter presents the security concepts terminologies (threat, risk, security risk management, se- curity risk management process, security threat model) and present the state of the art of security risk management models, compare and discuss strengths and weaknesses of such models. Then it presents the Mean Failure Cost (MFC) model for quantifying security threats as a rigorous measure of cyber security, and as a cascade of linear models in order to estimate the system security using the loss of a given stakeholders as a result of security breakdown. Finally it presents an overview of the applicabil- ity of the MFC measure to e-systems. In the conclusion, the chapter criticizes the MFC Cyber Security Measure and presents an overview of diferent perspectives. INTRODUCTION Actually the Internet is the main source of all threats and illegal activities. Consequently, E-systems are threatened exponentially, statistics have shown that organizations are currently investing in security resources. It has been shown that through 2005 the total global revenue for security products and ser- vice vendors amounted to $21.1 billion. Another source indicated that from 1999 to 2000, the number of organizations spending more than $ 1 million annually on security nearly doubled. So, expenditures have increased from 12% of all organizations revenues in 1999 to 23% in 2000 (Ekelhart et al., 2009). In fact, it is a challenging task for organizations to put the emphasis on security risk management in order to measure and assess security risk and provide a good plan for risk mitigation. The Rigorous Security Risk Management Model: State of the Art Neila Rjaibi Department of Computer science, Institut Supérieur de Gestion de Tunis (ISG), Tunisia Latifa Ben Arfa Rabai Department of Computer science, Institut Supérieur de Gestion de Tunis (ISG), Tunisia