Definition of "GCHQ"

For the challenge, GCHQ posted a code at www.canyoucrackit.co.uk and invited British citizens to solve it. The code consisted of 160 letters and numbers arranged in a rectangular display.

2013, Ravi Gupta, Hugh Brooks, Using Social Media for Global Security, page 190

I was inside Government Communications Headquarters, invariably called GCHQ. It's the UK's technical spy agency, only admitted to exist by the government in 1994.]

, William Heinemann