Hundreds of fans help cool computer servers at a Google data center in Mayes County, Okla. Google, Microsoft and other tech companies have been providing user data to the National Security Agency. Connie Zhou/Google via AP hide caption

itoggle caption Connie Zhou/Google via AP

The National Security Agency's headquarters in Fort Meade, Md. NSA/Reuters /Landov hide caption

itoggle caption NSA/Reuters /Landov

President Obama delivers a speech on national security Thursday at the National Defense University at Fort McNair in Washington. Pablo Martinez Monsivais/AP hide caption

itoggle caption Pablo Martinez Monsivais/AP

This image from the Federal Bureau of Investigation shows the remains of a pressure cooker that the FBI says was part of one of the bombs that exploded during the Boston Marathon. AP via FBI hide caption

itoggle caption AP via FBI