Obama defends U.S. surveillance effort as 'trade-off' for security

U.S. President Barack Obama listens to a student during a visit to Mooresville Middle School in Mooresville, North Carolina June 6, 2013. REUTERS/Kevin Lamarque

SAN JOSE, California (Reuters) - President Barack Obama on Friday staunchly defended the sweeping U.S. government surveillance of Americans' phone and internet activity, calling it a "modest encroachment" on privacy that was necessary to defend the United States from attack.

"Nobody is listening to your telephone calls. That's not what this program is about," Obama told reporters during a visit to California's Silicon Valley. He emphasized that the secret surveillance programs were supervised by federal judges and authorized by Congress, which had been briefed on the details.