Well the full message is
"436F6E67726174756C6174696F6E732C20796F7520736F6C766564207468652070757A7A6C65212057687920646F6E927420796F75206170706C7920746F206A6F696E206F7572207465616D3F206D69352E676F762E756B2F6361726565727320"
"Congratulations, you solved the puzzle! Why don�t you apply to join our team? mi5.gov.uk/careers "
So i doubt there is much more to it ;)