Lieutenant General Robert Elder, senior Air Force officer for cyberspace issues, recently joked that North Korea “must only have one laptop” to make the more serious point that every potential adversary – except Pyongyang – routinely scans US computer networks.

North Korea may be impotent in cyberspace, but its neighbour is not. The Chinese military sent a shiver down the Pentagon’s spine in June by successfully hacking into an unclassified network used by the top policy advisers to Robert Gates, the defence secretary.