The 9/11 terrorists, before their deadly attacks, sought invisibility through integration into the society they hoped to destroy. In a similar fashion, the terrorists who carried out subsequent attacks in Madrid and London attempted to blend into their host lands. This strategy has forced governments, including the United States, to rethink counter-terrorism strategies and tools.One of the current favored strategies involves data mining. In its pattern-based variant, data mining searches select individuals for scrutiny by analyzing large data sets for suspicious data linkages and pat-terns. Because terrorists do not “stand out,” intelligence and law enforcement agents want to do more than rely exclusively on investigations of known suspects...