Professor John Walker, managing director of forensics consultancy Secure-Bastion, said at the International Crime Science Conference in London last week that the Chinese government was behind the 'Titan Rain' attacks on the US and the UK.
The attacks were identified as coming from servers in China, but the Chinese government has never officially been accused of being behind the assault.
Professor Walker's claims will add to the paranoia about Chinese hackers attacking visitors and business people travelling to the Beijing Olympics.
The academic made his comments during a Q&A session when he was asked about state-sponsored terrorism. "This big problem has become more focused," he said.
"Up to last year people did not take it very seriously, and then there were state-sponsored Chinese groups and all sorts of groups attacking the UK and the US and getting into the infrastructure. That happened again earlier this year."
The International Crime Science Conference is organised by the Centre for Security and Crime Science at University College London. The Home Office is one of the conference sponsors.
Walker contributed to the House of Lords Science and Technology Committee's
report on Personal Internet Security published on 8 July.
"There is a problem with state-sponsored electronic terrorism," he told the audience.
"No matter how much collaboration you have internationally, if you have a state-sponsored terrorist coming out of China or Russia you are not going to get them.
"If they are state-sponsored e-criminals they are doing it for a purpose. And you cannot extradite them."
A formal complaint about Professor Walker's remarks was made to Gloria Laycock, director of the UCL Centre for Security and Crime Science.
Titan Rain is the name given by the US government to a coordinated series of attacks on US computer systems. Hackers gained access to many US computer networks, including those at Lockheed Martin and Nasa.