The British government’s ‘spy agency’ GCHQ has sent out their Christmas cards for the year which include a head-scratchingly-difficult cryptic puzzle that the public are encouraged to try and solve.

The cards, sent on behalf of GCHQ Director Robert Hannigan, contain a festive artwork as normal, as well as the traditional Christmas greeting. However, new for 2015, the card also contains a “grid-shading puzzle” and instructions on how people can attempt to complete it.

The prize for completing that puzzle? It will reveal an image that in turn leads to what GCHQ describe as a “series of increasingly complex challenges”. Alas, for those clever enough to complete all of the puzzles, they are invited to submit their entries from which one winner will be drawn.

Some have described it as Mr Hannigan’s plan to ensure those on his Christmas card list are doing their homework and keeping their brain sharp over the festive break, while others suggest it may eventually form part of a recruitment process.

Either way, it’s incredibly difficult. The public are invited to take part by visiting the GCHQ Christmas card page on its website (click here). You’re also encouraged to make a donation to the NSPCC.