Cyber-physical systems are the systems that combine the physical world with the world of information processing. CPS
involves interaction between heterogeneous components that include electronic chips, software systems, sensors and actuators. It
makes the CPS vulnerable to attacks. How to deal with the attacks in CPSs has become a research hotspot. In this paper we have
study the Architecture of CPS and various security threats at each layer of the archicture of CPS. We have also developed attack
taxonomy for CPS.