This study explores the significant impact of the internet on terrorism and extremism by focusing on three key areas: cyberterrorism, social media usage, and attack planning. Cyberterrorism has emerged as a major threat, with incidents such as the WannaCry ransomware attack highlighting its potential to disrupt critical infrastructures. The study reveals that the low cost and difficulty in tracing cyberterrorists contribute to its rising prevalence. Furthermore, social media has become a vital tool for extremist groups in that it facilitates global communication, recruitment, and propaganda dissemination. Events such as the Christchurch mosque attacks illustrate the challenges of monitoring extremist content online. The internet also aids in attack planning by providing discreet communication channels, easy access to materials, and simplified travel arrangements, as seen in the 9/11 and Manchester Arena bombings. Additionally, the chapter discusses how technological advancements have enhanced security agencies’ capabilities, leading to more effective prevention and response strategies. The findings highlight the dual role of the internet as both a facilitator of terrorism and a crucial asset in countering these threats.