Abstract: Critical infrastructures are vital assets for the public safety, economic welfare and national security of countries. Cyber systems are used extensively to monitor and control critical infrastructures. A number of infrastructures are connected to the internet via. corporate networks. Cyber security is therefore, an important item of the national security agenda of a country. These systems will empower our critical infrastructure and have the potential to significantly impact our daily lives as they form the basis for emerging and future smart services. On the other hand, the increased use of CPS brings more threats that could have major consequences for users but advances in technology make it necessary to develop new threats will continue to be exploited and cyber attacks will continue to emerge, hence, the need for new methods to protect CPS. This study introduces a novel framework for understanding cyber attacks and the related risks of multi elements, multi-layered to cyber-physical systems. The longer-term goal is to use the framework as a means to reduce cyber-physical system security properties and to enumerate the principles for designing systems that are resilient to cyber attacks and analysis of the security issues at the various layers of CPS architecture, risk assessment and techniques for securing CPS. Finally, challenges and possible solutions are presented and discussed.