The idea that the internet may enable an individual to become radicalized has been of increasing concern over the last two decades. Indeed, the internet provides individuals with an opportunity to access vast amounts of information and to connect to new people and new groups. Together, these prospects may create a compelling argument that radicalization via the internet is plausible. So, is this really the case? Can viewing ‘radicalizing’ material and interacting with others online actually cause someone to subsequently commit violent and/or extremist acts? In this article, we discuss the potential role of the internet in radicalization and relate to how cybersecurity and certain HCI ‘affordances’ may support it. We focus on how the design of systems provides opportunities for extremist messages to spread and gain credence, and how an application of HCI and user-centered understanding of online behavior and cybersecurity might be used to counter extremist messages. By drawing upon existing research that may be used to further understand and address internet radicalization, we discuss some future research directions and associated challenges.