In this excerpt from NOVA's "The Spy Factory," see how electronic information flows from Asia to the United States and how the National Security Agency is tapping into communications collected both from abroad and from within the U.S.

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Funding for NOVA is provided by ExxonMobil, David H. Koch, the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and public television viewers.

To learn more, visit http://www.pbs.org/nova/spyfactory