The need for computer and network security dates since the ’80-s of the last century. The first computer networks were local and in an academic setting, so there was large confidence among users associated with them (there were almost no security problems). With the sudden development of the information technology and the today’s Internet, the first abuses occurred along with the need to protect private and corporate data. Today, information safety is crucial and it is most evident especially in the e-commerce and e-business. The information is a vital corporate’s property and it has enormous value. The information security, primarily comprising computer and the network security, is mainly concerned with the data protection (privacy), data integrity and data availability. This edition covers main security concepts, such as authentication methods, intrusion detection and prevention, cloud security protocols, and cryptography.