With IoT era, development raises several significant research questions in terms of system architecture, design and improvement. For example; the requirement of virtual resource utilization and storage capacity necessitates making IoT applications smarter; therefore, integrate the IoT concept with cloud computing will play an important role. This is crucial because of very large amounts of data that IoT is expected to generate. The Cloud of Things (CoT) is used to connect heterogeneous physical things to the virtual domain of the cloud. Despite its numerous advantages, there are many research challenges with utilization of CoT that needs additional consideration. These include high complexity, efficiency, improving reliability, and security. This chapter introduces CoT, its features, the applications that use CoT. CoT, like all other networked functions, is vulnerable to security attacks. The security risks for CoT are listed and described. The security requirements for CoT are identified and solutions are proposed to address the various attacks on CoT and its components.