The three-day conference, which took place behind closed doors and under strict rules about confidentiality, was aimed at debating the line between privacy and security.

Among an extraordinary list of attendees were a host of current or former heads from spy agencies such as the CIA and British electronic surveillance agency Government Communications Headquarters, or GCHQ. Other current or former top spooks from Australia, Canada, France, Germany and Sweden were also in attendance. Google, Apple, and telecommunications company Vodafone sent some of their senior policy and legal staff to the discussions. And a handful of academics and journalists were also present.

According to an event program obtained by The Intercept, questions on the agenda included: "Are we being misled by the term 'mass surveillance'?" "Is spying on allies/friends/potential adversaries inevitable if there is a perceived national security interest?"