The response to these revelations was the 1978 Foreign Intelligence Surveillance Act, or FISA - a law that set judicial procedures for requesting electronic surveillance of persons thought to be engaged in espionage or terrorism against the US.
Today the NSA is in the curious position of being both secretive and famous. Its work remains so closely held that its director seldom appears in public. Yet it has starred (as the villain) in at least one recent feature-length movie, "Enemy of the State." The NSA itself, perhaps to bolster its image, has created a website for children, which features the Cryptokids, an assortment of cartoon animal characters who, in games, carry out code-breaking assignments and other espionage activities.
Following the fall of the Berlin Wall, and the loss of the agency's cold-war mission of eavesdropping on everything from Soviet missile telemetry to the car-phone calls of Kremlin leaders, the NSA lost about one-third of its budget, and one-third of its manpower.
At the same time, in the decade of the 1990s the world saw an explosion in what NSA experts call "packetized communications" (what the rest of the world calls e-mail and other computer missives). Also, cellphone use increased 50 times over in the '90s, noted General Hayden, now principal deputy director of national intelligence, in a 2002 congressional hearing. US international phone calls went from 38 billion minutes to over 100 billion minutes annually.
Faced with a new enemy - Al Qaeda - that communicated as little as possible, and in constantly changing ways, the NSA was forced to become "hunters rather than gatherers," in a phrase used by its former director of signals intelligence, Maureen Baginski.
Today, Ms. Baginski has moved on. In 2003, she was named the FBI's first-ever executive assistant director of intelligence. And the NSA is under fire for what critics deem is hunting for intelligence a bit too much.
Under the domestic eavesdropping program - administration officials prefer to call it a "terrorist surveillance program" - the NSA since 2002 has been listening in on international communications of some people in the US, when those communications are thought to be connected to possible terror activity.