ABSTRACT
The Cambridge Dictionary describes the term "challenge" as "Something needing great mental or physical effort in order to be done successfully." This definition is too generic and lead to nowhere. This chapter develops the definition and makes it compatible with Smart Cities. It discusses the new paradigm of digital immunity as a futuristic adaptive defense with a different approach to shield Smart Cities from all evil. Smart Cities are already immersed in the generation of Internet of Everything, smart mobile, smart meters, smart sensors, smart traffic control, machine-to-machine, wearable devices, big data, the cloud, and critical infrastructure systems. Antivirus technologies providers have to jump on the artificial intelligence and nanotechnology bandwagon and develop cognitive and predictive expert systems in order to protect an "airtight" Smart City. Building an ecologically Smart City is quite a challenging endeavor. A Smart City is a space where citizens live and breathe, and are strapped to the Internet.
