In this chapter we discuss technical issues regarding intelligence and security informatics (ISI) research towards accomplishing the critical missions of international security and counterterrorism. We propose a research framework addressing the technical challenges facing counterterrorism and crime-fighting applications, with a primary focus on the knowledge discovery from databases (KDD) perspective. We also present several Dark Web-related case studies in collecting, analyzing and visualizing open-source terrorism information. Using a web spidering approach, we have developed a large-scale, longitudinal collection of extremist-generated Internet-based multimedia and multilingual contents. We have also developed selected computational link analysis, content analysis, and authorship analysis techniques to analyze the Dark Web collection.