Transcript for Hunting the NSA Leaker
Fallout from that revelation that America's phone records and also Internet searches are under surveillance by the government. The president arriving tonight in California. For a summit with the leader of China. But before he left to spend much of the day fighting back saying the surveillance is about national security. -- -- chief investigative correspondent Brian Ross. That law enforcement authorities expect a full court press at the NSA and other spy agencies to find the leaker who they called no hero. There are only a few senior -- who would have had access to all the documents made public in the Washington Post and the guardian. I don't welcome weeks. Because. There's a reason why these programs are classified. The president was forced to publicly acknowledge and defend the two spy programs that had operated in secrecy for seven years. Monitoring the Internet traffic of foreigners and collecting the phone records of every American. When it comes to telephone calls. Nobody is listening to your -- uncles. And the president said what he called the modest encroachments on privacy were worth it they help us prevent terrorist attacks. US counterterrorism officials told ABC news today. The Internet spy program helps stop this American al-Qaeda operative Najibullah zazi. From planting bombs on the New York City Subway system for years ago. Officials said the trial began in Britain with the arrest of a terrorist suspect he -- Internet messages led to an al-Qaeda coordinator and Pakistan. And then his emails led desires -- Denver where he was two weeks away from -- -- when he sent the message the marriage is ready without that intercept. He would have conducted attacks in New York City. But critics say he could have been stopped without such a broad reaching surveillance program. Still for all the talk about intrusions of privacy. Internet companies still lost more about Americans -- the government. Google even uses what it calls an automated government completely go through Gmail messages -- look for its key words in order to tailor it's ads to customers costs as its rival Microsoft points out in this Internet -- Every word. In every email. To and from every want to sell pads -- on your most personal messages. Google says no human ever reads the Jim -- of its customers the same thing the president said today about the government's secret monitoring phone records and Internet traffic. Just a modest encroachment of privacy caught in this online world thank you so much Brian.
This transcript has been automatically generated and may not be 100% accurate.