NOVA exposes the hidden world of high-tech, 21st-century eavesdropping carried out by the National Security Agency (NSA). Today, the NSA is the world's largest intelligence agency, three times the size of the CIA and far more secret. Its mission is to eavesdrop on the world - from cell phones in Europe to pay phones in Afghanistan to email messages from Pakistan to Baghdad. But since 9/11, it also has turned its giant ear inward, listening in without warrant on thousands of American citizens, many of whom are on the government's secret watch list, now more than half-a-million names long. Based on the latest best-seller by journalist James Bamford, "The Spy Factory" is a gripping investigation of the NSA, from its tragic failures leading up to the 9/11 attacks to its secret listening rooms currently installed in the nation's telecom facilities. The program presents groundbreaking new evidence about how the agency listened in to the phone calls of key 9/11 plotters, yet failed to realize they were located in the U.S. To show how current eavesdropping technology works, NOVA traces the path of an email sent from Asia to the U.S. via fiber optic cables on the Pacific sea floor. From a beach in California, the email then travels to a telecom switching facility in San Francisco, where the cables are covertly duplicated, with one copy of everything - including the original email - going to the NSA's secret room and the other transmitted to its proper destination. This is a suspenseful and eye-opening report on the threat to privacy and the effectiveness of high-tech surveillance in the age of terrorism.