gchq christmas puzzle
GCHQ's Christmas shading puzzleGCHQ

If you happen to be on the Christmas card list of GCHQ Director Robert Hannigan, then you'll be getting a little brain teaser along with your annual festive greetings from the department. The grid shading puzzle is the first step in a series of increasingly complex challenges.

If you manage to get through all the stages, you are invited to submit an answer via a designated GCHQ email address, with the winners announced in early 2016.

For those of us who haven't quite made it onto Mr Hannigan's card list, we can still take part – the first puzzle grid is shown above and the instructions are as follows:

"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."

Those enjoying the puzzle are also invited to make a donation to the National Society for the Prevention of Cruelty to Children.