
Officials in Whitehall did not reveal when and how the attack took place.
This latest cyber strike follows recent reports in the Financial Times that US government figures believe the Chinese military, including members of the Chinese People’s Liberation Army (PLA), was behind the Pentagon military computer network hack in June.
US officials said a malicious user penetrated one of the email servers of the defence headquarters, which took more than 1,500 computers offline.
The attack caused administration problems and the Pentagon shut down the network for more than a week while the hacks continued, according to a spokesperson for the American defence department.
However, China has officially denied responsibility for either of the hacking attacks.
Gary McKinnon allegedly hacked into the US military and NASA computer systems back in 2001. Authorities in the US accuse the 40-year-old Scot of hacking into 97 computers, including those of the Pentagon. He lost his fight against extradition to America in April.