of data and the manner in which the data are aggregated, and about the possibility that the government could, through its collection and analysis of data, inappropriately influence individuals’ conduct. Intruding on privacy also risks ignoring constitutional concerns about general search, as reflected in the Fourth Amendment. The committee strongly believes that such intrusion must be minimized through good management and good design, even if it cannot be totally eliminated.

The difficulty of detecting the activity of terrorist groups through their communications, transactions, and behaviors is hugely complicated by the ubiquity and enormity of electronic databases maintained by both government agencies and private-sector corporations. Retained data and communication streams concern financial transactions, medical records, travel, communications, legal proceedings, consumer preferences, Web searches, and, increasingly, behavioral and biological information. This is the essence of the information age—it provides us with convenience, choice, efficiency, knowledge, and entertainment; it supports education, health care, safety, and scientific discovery. Everyone leaves personal digital tracks in these systems whenever he or she makes a purchase, takes a trip, uses a bank account, makes a phone call, walks past a security camera, obtains a prescription, sends or receives a package, files income tax forms, applies for a loan, e-mails a friend, sends a fax, rents a video, or engages in just about any other activity. The proliferation of security cameras and means of tagging and tracking people and objects increases the scope and nature of available data. Law-abiding citizens leave extensive digital tracks, and so do criminals and terrorists.

Gathering and analyzing electronic, behavioral, biological, and other information can play major roles in the prevention, detection, and mitigation of terrorist attacks, just as they do against other criminal threats. In fact the U.S. government has increased its investment in counterterrorism programs based on communications surveillance, data mining, and information fusion. Counterterrorism agencies are particularly interested in merging several different databases (information fusion) and then probing the combined data to understand transactions and interactions of specific persons or organizations of interest (data mining). They would also like to identify individuals (through data mining and behavioral surveillance) whose transactions and behavior might indicate possible terrorist links.

Such techniques often work well in commercial settings, for example for fraud detection, where they are applied to highly structured databases and are honed through constant use and learning. But the problems confronting counterterrorism analysts are vastly more difficult. Automated identification of terrorists through data mining (or any other known

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