This thesis considers the structural characteristics of online criminal networks from a technical and an economic perspective. Through large-scale measurements, we empirically describe some salient elements of the online criminal infrastructures, and we derive economic models characterizing the associated monetization paths enabling criminal profitability. This analysis reveals the existence of structural choke points: components of online criminal operations being limited in number, and critical for the operations’ profitability. Consequently, interventions targeting such components can reduce the opportunities and incentives to engage in online crime through an increase in criminal operational costs, and in the risk of apprehension. We define a methodology describing the process of distilling the knowledge gained from the empirical measurements on the criminal infrastructures towards identifying and evaluating appropriate countermeasures. We argue that countermeasures, as defined in the context of situational crime prevention, can be effective for a long-term reduction in the occurrence of online crime.