GCHQ Has Included A Brainteaser In Its Christmas Cards

    No spoilers, because we can't solve it either. Update: GCHQ has now released the answers.

    Kelly Oakes
    by Kelly Oakes

    BuzzFeed Staff, UK

    GCHQ's Christmas cards this year include a cryptic twist in the form of this puzzle.

    GCHQ

    The cards were sent out to a select few people, but you can download a printable version of the puzzle here (once everyone else stops trying to – the site currently appears to be down).

    Its website explains:

    In this type of grid-shading puzzle, each square is either black or white. Some of the black squares have already been filled in for you.

    Each row or column is labelled with a string of numbers. The numbers indicate the length of all consecutive runs of black squares, and are displayed in the order that the runs appear in that line.

    For example, a label "2 1 6" indicates sets of two, one and six black squares, each of which will have at least one white square separating them.

    Some are taking the brainteaser more seriously than others.

    Tom Cheshire @chesh

    Solved it. Classy move of GCHQ to play tribute to @Snowden with their xmas puzzle.

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    But so many people tried to download the puzzle that the website appears to have been down for most of the morning.

    Alex Macpherson @alex_macpherson

    have GCHQ crashed their own website under the traffic to their Xmas puzzle? the cutting edge of online security there

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    If you want some hints, this Reddit thread is a good place to start.

    And if you do manage to complete all stages of the puzzle, send your solution to GCHQ by the end of January.

    BBC / giphy.com

    Then do a little dance.

    UPDATE: GCHQ has now published the answers to the puzzle.

    GCHQ

    It said that more than half a million people attempted the brainteaser.

    The grid shading stage created a QR code which led to puzzles on a page of the GCHQ website testing participants "analytical prowess and knowledge of phonetics, semaphore, French, snooker, The Lord of the Rings" and more.

    No-one found all of the answers, but three people came close and will be awarded with a GCHQ paperweight and an Alan Turing biography for their efforts.