The detailed records – which cannot be independently verified – show specific dates and the IP addresses of computers in Hong Kong and on the mainland hacked by the National Security Agency over a four-year period.

They also include information indicating whether an attack on a computer was ongoing or had been completed, along with an amount of additional operational information.

The small sample data suggests secret and illegal NSA attacks on Hong Kong computers had a success rate of more than 75 per cent, according to the documents. The information only pertains to attacks on civilian computers with no reference to Chinese military operations, Snowden said.

“I don’t know what specific information they were looking for on these machines, only that using technical exploits to gain unauthorised access to civilian machines is a violation of law. It’s ethically dubious,” Snowden said in the interview on Wednesday.