Network security involves protecting computer networks from unauthorized access, misuse, and hacking. It is important because we rely on computer networks to manage critical systems like banking, utilities, healthcare, and more. Effective network security requires identification of users, authenticating users, and controlling user access through measures like strong passwords, antivirus software, encryption, firewalls, backups, auditing systems, security training, and testing security systems. Some common threats to network security include viruses, Trojan horses, spam, phishing, password attacks, and insecure shared computers.