The document discusses network security and its importance in protecting computer networks from breaches and threats. It defines network security as using both software and hardware to protect the integrity, confidentiality, and accessibility of computer networks and data through technologies, devices, processes, and configuration rules. The document then describes common network security attacks, including passive attacks that involve monitoring and data theft and active attacks that modify or damage data. It concludes by outlining various types of network security measures, such as access control, antivirus software, firewalls, data loss prevention, and mobile device security.