No spoilers, because we can’t solve it either.
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).
GCHQ
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.
