Hundreds of thousands of brain teaser buffs from around the world have been trying to solve the puzzle released by a British intelligence agency in its annual Christmas card to staff last December.
The agency – the Government Communications Headquarters (GCHQ) – posted the first stage of the puzzle online more than two months ago.
When the grid-shading game is complete, a QR code becomes visible that leads to an increasingly difficult series of challenges.
“In this first grid-shading puzzle, each square is black or white,” the GCHQ website states.
“Some of the black squares have already been filled in for you.
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“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.”
GCHQ has revealed nearly 600,000 people have solved the first stage of the game but just 30,000 have made it through to the final round. Of these, none have solved it.
“It’s not as abstract as you think.” GCHQ Director Robert Hannigan said.
The solution will be published on the GCHQ website in early February.
