Internet-of-Things (IoT) is applied in many contexts, Industrial IoT (IIoT) is one such example. This chapter explores the security issues and challenges in IIoT. Cloud Computing is significantly influencing the architectural and implementation factors for IoT. Due to the nature of Cloud and IoT architectures and infrastructures, it is important to consider distributed and Decentralised Computing. With the focus on security aspects and concerns in IIoT, this chapter presents a discussion on Decentralised Computing and security concerns of Decentralised Computing from a Cloud Computing and IoT perspective. The chapter introduces the concept and definitions of Cloud Computing, Decentralised Computing, and IoT. It also addresses how Decentralised Computing is an approach to implement Cloud Architecture and IoT infrastructure, and how Cloud and IoT security concerns affect the deployment of a decentralised architecture. The above security and implementation aspects of Decentralised Computing, Cloud Computing and IoT are mapped into the context of IIoT.