GCHQ has revealed that not one person was able to solve its Christmas codebreaker puzzle.
The agency's director, Robert Hannigan, included the challenge in his Christmas card, and later opened it up to the public.
More than half a million people tried unsuccessfully to solve it, and with nobody able to complete the challenge, GCHQ has today released the solutions.
The five-stage challenge combined problem-solving, linguistic and maths puzzles, which got progressively more difficult.
Three people were able to get close, including a man from Scotland and a man from Belgium.
A third person also did well, but the agency gave no details about their identity.
All three will be rewarded with a GCHQ paperweight and a copy of the biography of Bletchely Park codebreaker Alan Turing, which will be signed with a personal message from Mr Hannigan.
GCHQ has been known to release puzzles in the past to recruit cryptographers to the agency.