Internet of Things (IoT) is an emerging concept in smart infrastructures describing a wide ecosystem where interconnected devices and services collect, exchange and process data in order to adapt dynamically to a context. IoT is tightly bound to cyber-physical systems and in this respect is an enabler of Smart Infrastructures by enhancing their quality of service provisioning. Smart infrastructure, enabled by technologies like IoT, offer numerous of advantages bringing serious cost savings and efficiencies. These kinds of data-driven environments, fueled by connected devices and network connectivity, become a new attack surface for cyber threats. Cyber security approaches develop guidance to secure IoT and Smart Infrastructures from cyber threats, by highlighting good security practices and proposing recommendations to operators, manufacturers and decision makers. In this paper, cyber security approaches are analyzed in a smart city infrastructure.