The FBI is investigating after the Chinese government hacked a US Navy contractor and stole highly sensitive security data, US media say.
Data stolen in the breach include plans for a supersonic missile project, US officials told the Washington Post.
The attacks, in January and February this year, were confirmed by CBS News.
Hackers targeted a contractor linked to a US military organisation that conducts research and development for submarines and underwater weaponry.
In a separate development, a former US intelligence officer was convicted on charges of giving top-secret documents to a Chinese agent.
Kevin Mallory, 61, was found guilty under the federal Espionage Act on Friday. He is due to be charged on 21 September and faces a maximum penalty of life in prison, the US justice department said in a statement.
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