The state broadcaster’s investigative Four Corners programme said the attack on a contractor involved with building the new Canberra headquarters of the Australian Security Intelligence Organisation was traced to a server in China.

It cited security experts as saying the theft exposed the agency to being spied on and may be responsible for a cost-blowout and delays to the opening of the building, which was supposed to be operational last month.

Des Ball, from the Australian National University’s Strategic and Defence Studies Centre, said the blueprints would show which rooms were likely to used for sensitive conversations, and how to put devices into the walls.

“Once you get those building plans you can start constructing your own wiring diagrams, where the linkages are through telephone connections, through wi-fi connections,” he was quoted as saying.