Under a system codenamed ECHELON

Under a system codenamed ECHELON – launched in the 1970s to spy on Soviet satellite communicating – the NSA and its (very) junior partners in Britain, New Zealand, and Canada operate a network of massive, highly automated interception stations, covering the globe amongst them. In multiple ways, each of the countries involved is breaking its own laws, those of other countries, and international law - the absence of court – issued warrants permitting surveillance of named individuals is but one example. But who is to stop them?
In 1999, the House Intelligence Committee of the US Congress sought internal NSA documents about its compliance with the law that prohibits it from deliberately eavesdropping on Americans, either in the United States or overseas, unless the Agency can establish probable cause to believe that they are agents of a foreign government committing espionage or other crimes: NSA stonewalled the committee.
Apart from specifically targeted individuals and institutions, the ECHELON system works by indiscriminately intercepting very large quantities of communications and using computers to identify and extract messages of interest from the mass of unwanted ones. Every intercepted message – all the embassy cables, the business deals, the sex talks, the birthday greetings – is searched for keywords, which could be anything the searchers think might be of interest. Computers can “listen” to telephone calls and recognize when keywords are spoken. Those calls are extracted and recorded separately, to be listened to in full by humans. The list of specific targets at any given time is undoubtedly wide – ranging, at one point including the likes of Amnesty International and Christian Aid.
From the book 'Rogue State' by William Blum