Nowadays, the Internet has become all pervasive in the daily life around the world, transforming the old telephone set into a small multipurpose computer. Consequently, human life has radically changed. Our dependence on computer networks became undeniable and together with it, harmful programs or malwares, developed to damage machines or to steal information, represent permanent threat to individuals and society. In computer science a new work research line emerged: cyber-security, which includes developing models, routines and software to protect machines and networks from malicious programs. This new discipline has attracted researchers to develop ideas for protecting people and corporations. Cyber-security is the object of this book, that presents hints about how the community is working to manage these threats: Mathematical models based on epidemiology studies, control of malwares and virus propagation, protection of essential service plants to assure reliability, the direct impact of virus and malwares over human activities and behavior, Government entities which are highly concerned with the necessary preventive actions.