The diverse applications of IoT are achieved by a set of complex inter-related networks of things and communications. IoT applications are also concerned about an array of devices such as sensors, mobile devices, personal computers, the smart systems such as Alexa, Eco, etc, besides the whole range of communication network binding them together in a seamless manner. This book explores the variegated perspectives of security in the complex context of Internet of Things. It also aims to present the changing face of security, from the ubiquitous networks comprising of WSN as the lowest layer, to the enabler apps working as bridge between the users and the complex IoT system. It takes a closer look at the different types of security schemes required to fit in the heterogeneous nature of IoT network., whilst the readers are also introduced to basic attacks targeting an IoT network, as well as specific types of security schemes worked out by researchers across different countries. As Programmable Logic Controllers (PLC) play a fundamental role in Industrial Control Systems, since they provide various functionalities of physical tools by collecting data from input devices and sending commands to output devices, this book includes a discussion on the security considerations of extending a PLC-based system with IoT capabilities. Other advanced topics include: The machine ethics aspects in the IoT system; the Intrusion detection of WSN; and the methods of securing the user from privacy breaches due to the overprivileged IoT apps. This book will be beneficial to any readers interested in security of IoT systems and how to develop a layer-wise security scheme for such a system.