The threat from radical Islamic extremists affiliated with terrorist organizations represents a serious challenge to the security of South East Europe (SEE). Although there are different opinions about the reality of the threat empirical evidence unequivocally confirm that individuals and groups affiliated with terrorist organizations are present in the region, work and act against its security. In the past several years, individuals and groups affiliated with radical Islamic extremists that practice terrorism have utilized their actions to the South East European cyberspace. Their malicious agenda uses technical, social, normative-legal, and the existing challenges of modern day societies. At the same time, even though all of the South East countries have developed effective counter-terrorist measures, none of these countries have address terrorists' and their affiliates' use of a cyberspace. The chapter briefly addresses the reality of the threat posed by the radical Islamic extremists affiliated with terrorists' organizations. Then it explores how this individuals and groups use/abuse cyberspace to further their agenda. Finally, it provides some recommendation that South East governments need to consider if they are about to protect their societies and Euro-Atlantic values.