How dare you post a recruitment microsite for GCHQ, poor taste, Sir, poor taste.
For instance, OP might have found it surprising that GCHQ would post such a challenge amidst all the controversy.
Obviously SIGINT for a nation isn't a bad thing per se, but when they infringe on the core democratic principles of the state they claim to represent then that's just a disgusting abuse of power.
I do agree that there have been gross abuses of power committed over the past years, but this isn't necessarily something that should be the center of a debate on it. Especially since they aren't forcing you to apply to a job by participating in this challenge.