Echelon intercepts and processes international communications via passing communications satellites. It is part of a global surveillance system that is now over 50 years old. The US National Security Agency (NSA) and Britain's Government Communications Headquarters (GCHQ) run the system. The purpose of the network is to collect signals intelligence (Sigint) by covertly intercepting foreign and international communications. Other parts of the Sigint system intercept messages from the Internet, from undersea cables, from radio transmissions, from secret equipment installed inside embassies, or use orbiting satellites to monitor signals anywhere on the earth's surface. The system includes stations run by the United States, Britain, Canada, Australia and New Zealand. They can access and process almost all of the worlds satellite communications, automatically analysing and relaying it to 'customers' who may be continents away. Not all of the stations use the same codename. But all are part of the same integrated global network using the same equipment and methods to extract information and intelligence illicitly from billions of messages every day, all over the world. Under a secret agreement signed in 1947, called UKUSA, the English-speaking countries agreed to share responsibility for overseeing surveillance in different parts of the world. Britain's zone included Africa and Europe, east to the Ural Mountains of the former USSR; Canada covered northern latitudes and Polar regions; Australia covered Oceania. The agreements prescribed common procedures, targets, equipment and methods that the Sigint agencies would use. Other countries including Norway, Denmark, Germany and Turkey later signed Sigint agreements with the United States and Britain.

The Power of the NSA:
• On 6 September 1960, two NSA defectors held a press conference and revealed the worldwide scope of NSA's activities: "We know from working at NSA [that] the United States reads the secret communications of more than forty nations, including its own allies... Both enciphered and plain text communications are monitored from almost every nation in the world, including the nations on whose soil the intercept bases are located."
• Fifteen years later, US senator Frank Church issued a grim warning at the start of the post-Watergate investigations into NSA. Church's committee then uncovered how NSA had maintained a "watch list" to trap the international communications of thousands of Americans, including prominent opponents of the Vietnam war. "I know the capacity that is there to make tyranny total... we must see to it that this agency... operate[s] within the law and under proper supervision, so that we never cross over that abyss."

The Echelon network was developed in the late 1960s. It was planned after dozens of countries agreed in 1964 to establish the International Telecommunications Satellite Organisation (Intelsat). Intelsat would own and operate a global constellation of communications satellites, providing long distance and intercontinental links. By 1966, the first Intelsat satellites were in orbit. The UKUSA intelligence agencies resolved to ensure they always had access to private messages sent on Intelsats. But the only way to intercept all the satellite traffic was for NSA and GCHQ secretly to build their own shadow ground stations. In 1971, GCHQ started operating a secret new station at Morwenstow, near Bude in Cornwall, England. It intercepted satellite communications over the Atlantic and Indian Oceans. To intercept Pacific regional communications, NSA built a second station at Yakima, near Seattle in the north-west of the US. Now a key feature of each station is the use of computers called Dictionaries, which automatically select written (but not speech) communications using lists of target numbers, subjects and "keywords" of intelligence interest. The world's Echelon sites

• The Yakima station near Seattle in the US.
• The Sabana Seca station in Puerto Rico.
• The Skibsbylejren station in Denmark.
• The Sugar Grove station in West Virginia in the US.
• The Waihopai station in New Zealand.
• The Leitrim station in Canada.
• The Australian station.
• The Cypriot station.
• The Dutch station.

Other communications are intercepted directly from landlines. In 1991, the British television programme World in Action reported on the operations of one Dictionary computer at GCHQ's London station in Palmer Street, Westminster (station UKC1000). The programme quoted GCHQ employees, who spoke off the record: "Up on the fourth floor there, [GCHQ] has hired a group of carefully vetted British Telecom people... It's nothing to do with national security. It's because it's not legal to take every single telex. And they take everything: the embassies, all the business deals, even the birthday greetings, they take everything. They feed it into the Dictionary." Starting in 1981, NSA and GCHQ also built the first large global digital wide area network (WAN). Until the mid 1990s, this international network connecting Sigint stations and processing centres was larger than the Internet. The network is connected over transoceanic cables and space links. Most of the capacity of the American and British military communications satellites, Milstar and Skynet, is devoted to relaying intelligence information. The largest electronic spying base in the world is NSA Field Station F83 at Menwith Hill, Yorkshire. Known internally as SILKWORTH, it is one of four primary centres for operating and processing data from Sigint satellites, which listen from space. Its second major function, known as MOONPENNY, is to intercept data from other country's satellites, military or civil. NSA Field Station F81 at Bad Aibling, Bavaria, Germany operates the GARLICK system, which also intercepts satellite communications. Other stations are at Denver, Colorado and Pine Gap, near Alice Springs in Australia. Canada, Australia and New Zealand agreed to join the Echelon system in the mid 1980s. Australia's site near Perth in western Australia now includes four interception dishes. The New Zealand site, Waihopai station, has two dishes targeted on Intelsat satellites covering the south Pacific. In 1996, a New Zealand TV station obtained images of the inside of the Waihopai station's operations centre. The pictures were obtained clandestinely by filming through partially curtained windows at night. The TV reporter was able to film close-ups of technical manuals held in the control centre. These were Intelsat technical manuals, providing confirmation that the station targeted the civilian satellites. The cameras showed that the station was virtually empty, and operated fully automatically under computer control. In 1992, then NSA director, vice admiral William O Studeman, described NSA's goals and said that the agency's job was to provide America with "global access". In March 1999, the Australian government admitted for the first time that reports of the secret UKUSA spying treaty were true. They confirmed that their Sigint organisation, the Defence Signals Directorate (DSD) "does cooperate with counterpart signals intelligence organisations overseas under the UKUSA relationship". Even Britain's Sigint agency GCHQ now has a web site. It boasts that it helps operate "one of the largest WANs [Wide Area Networks] in the world" and that "all GCHQ systems are linked together on the largest LAN in Europe... connected to other sites around the world". The same Web pages also claim that "the immense size and sheer power of GCHQ's supercomputing architecture is difficult to imagine". Go to ZDNet's Echelon Special The British are keeping a stiff upper lip, the US simply avoid mentioning it and the French believe it has been stealing secrets from France for years. Go to the TalkBack forum to tell us what you know and think about Echelon.