This page from GCHQ’s internal GCWiki, dated 24 April 2012 describes procedures for searching through financial data retained by the agency, and cites examples of some of its sources: see the Intercept article Airport Police Demanded An Activist’s Passwords. He Refused. Now He Faces Prison In The UK, 23 September 2017.
This 13 September 2010 presentation from the NSA’s OTP VPN Exploitation Team explains the work of the division: see the Der Spiegel story Prying Eyes: Inside the NSA’s War on Internet Security, 28 December 2014.
This post dated 20 December 2005, taken from the NSA’s internal newslatter Foreign Affairs Digest, describes the assistance rendered to Turkey against Kurdish nationalists, particularly the PKK, and describes the difficulties of reconciling this with US strategic interests in Iraq: see the Intercept article How the NSA Helped Turkey Kill Kurdish Rebels, 31 August 2014.