# Network Security and Common Network Threats Network security refers to the collection of policies, practices, technologies, and procedures used to protect computer networks, connected devices, data, applications, and communication resources from unauthorized access, misuse, disruption, modification, or destruction. In network programming and administration, security is an essential responsibility because networks provide the infrastructure through which users, applications, servers, and devices communicate. A secure network aims to maintain confidentiality, integrity, availability, authentication, and accountability of information and services. Network security protects data while it is being transmitted as well as while it is stored or processed on network-connected systems. Network administrators implement security controls such as access control, firewalls, intrusion detection systems, secure protocols, encryption, authentication mechanisms, VPNs, and regular software updates. Effective security also requires continuous monitoring, vulnerability assessment, backup procedures, and user awareness because threats constantly evolve. One of the common threats to a network is a virus. A virus is a malicious program that attaches itself to legitimate files or programs and spreads when the infected file is executed or shared. Viruses may corrupt files, delete data, modify system configurations, consume resources, or provide unauthorized access to attackers. For example, an infected executable file downloaded from an untrusted source may spread to computers across an organization when employees execute it. Antivirus software, endpoint protection, regular patching, restricted user privileges, and safe handling of files help reduce the risk of virus infections. A worm is another major network threat. Unlike a traditional virus, a worm can reproduce and spread automatically across networks without necessarily requiring a user to execute an infected file. Worms commonly exploit vulnerabilities in operating systems, network services, or applications. Once one computer becomes infected, the worm can scan the network for vulnerable systems and rapidly spread to them. This can consume bandwidth, overload servers, slow network performance, and sometimes install additional malicious software. Network administrators can reduce worm propagation through security patches, network segmentation, access controls, intrusion prevention systems, and continuous monitoring of unusual network traffic. Denial-of-Service (DoS) attacks attempt to make a network service, server, or application unavailable to legitimate users. An attacker may send an excessive number of requests or specially crafted traffic so that the target exhausts its processing power, memory, bandwidth, or connection capacity. A Distributed Denial-of-Service (DDoS) attack is more powerful because traffic originates from many compromised computers or devices, commonly called a botnet. Since the attack traffic comes from multiple sources, blocking a single attacking