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The puzzle is all about shading certain squares black and leaving others white.
The numbers on the side of the grid indicate how many consecutive black squares there will be in each row or column. There has to be at least one white square between each run of black squares.
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.
Once all stages have been unlocked and completed successfully, players are invited to submit their answer via a given GCHQ email address by 31 January 2016. The winner will then be drawn from all the successful entries and notified soon after