ECHELON in the context of Uplink

Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of signals, whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). As classified and sensitive information is usually encrypted, signals intelligence may necessarily involve cryptanalysis (to decipher the messages). Traffic analysis—the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis.

The Five Eyes (FVEY) is an Anglosphere intelligence alliance comprising Australia, Canada, New Zealand, the United Kingdom, and the United States. These countries are party to the multilateral UKUSA Agreement, a treaty for joint cooperation in signals intelligence. Informally, "Five Eyes" can refer to the group of intelligence agencies of these countries. The term "Five Eyes" originated as shorthand for a "AUS/CAN/NZ/UK/US Eyes Only" (AUSCANNZUKUS) releasability caveat.

The origins of the FVEY can be traced to informal, secret meetings during World War II between British and American code-breakers that took place before the US formally entered the war. The alliance was formalized in the post-war era by the UKUSA Agreement in 1946. As the Cold War deepened, the intelligence sharing arrangement was formalised under the ECHELON surveillance system in the 1960s. This system was developed by the FVEY to monitor the communications of the Soviet Union and Eastern Bloc; it is now used to monitor communications worldwide. The FVEY expanded its surveillance capabilities during the course of the "war on terror", with much emphasis placed on monitoring the Internet. The alliance has grown into a robust global surveillance mechanism, adapting to new domains such as international terrorism, cyberattacks, and contemporary regional conflicts.