China army unit 'behind prolific hacking'
19 February 2013 Last updated at 15:40 GMT
A secretive branch of China's military is probably one of the world's "most prolific cyber espionage groups", a US cyber security firm has said.
Mandiant said Unit 61398 was believed to have "systematically stolen hundreds of terabytes of data" from at least 141 organisations around the world.
It traced the attacks to the doorstep of a non-descript building in Shanghai used by the unit.
John Sudworth reports.