This undated GCHQ presentation gives an overview of the agency’s use of hacking techniques, including an explanation of what it perceived the legal position to be at the time: see the InterceptHow U.K. Spies Hacked a European Ally and Got Away With It, 17 February 2018.
This undated dictionary produced by NSA Special Source Operations, provides glosses for several terms associated with the corporate partner FAIRVIEW, including the AT&T-specific term ‘SNRC’: see the New York Times article AT&T Helped U.S. Spy on Internet on a Vast Scale, 15 August 2015.
This undated GCHQ reference document enumerates the processes and tools analysts use for computer network exploitation: see the Der Spiegel article The Digital Arms Race: NSA Preps America for Future Battle, 17 January 2015.
This undated page taken from GCHQ’s internal GCWiki cites the codename LEGSPIN (highlighted) also found in an analysis of Regin malware: see the Intercept article Operation Socialist: The Inside Story of How British Spies Hacked Belgium’s Largest Telco, 13 December 2014.