US media report Chinese government hackers took more than 600 gigabytes of data, including plans for anti-missile ship.

Chinese government hackers breached a US naval contractor and made off with more than 600 gigabytes of data, American officials speaking to two US media outlets said.

The breaches occurred in January and February and affected a contractor working on submarines and underwater weapons, the Washington Post first reported on Friday.

The Post said that those behind the breach are alleged to have obtained secret plans for a supersonic anti-ship missile. The newspaper reported that while the data was housed on the contractor’s unclassified network, when aggregated, officials said the data could be considered classified.

According to the New York Times, the data taken was unclassified.

Both media outlets cited unnamed officials and the contractor targeted in the cyber attack was not identified by either.

Officials told the newspapers that there is an ongoing investigation into the breach by the US Navy and the FBI.

“Per federal regulations, there are measures in place that require companies to notify the government when a ‘cyber incident’ has occurred that has actual or potential adverse effects on their networks that contain controlled unclassified information. It would be inappropriate to discuss further details at this time,” the US Navy said in a statement to the Reuters news agency.

The Chinese embassy told Reuters that it knew nothing about the reported hacking, adding that the Chinese government “staunchly upholds cybersecurity, firmly opposes and combats all forms of cyber attacks in accordance with law”.

Cyber warfare capabilities

Alongside other countries, including the US, China is believed to have significant offensive cyberwarfare capabilities.

In 2011, Canada blamed Beijing for a breach of several government networks, including its department for Defence Research and Development.

US prosecutors indicted five Chinese nationals linked to the People’s Liberation Army Unit 61398 in 2014 over claims they breached several companies in order to steal business secrets.

For its part, the US is also accused of hacking Chinese government and public interests.

The US National Security Agency whistle-blower, Edward Snowden, said the US government was hacking Chinese mobile phone companies and research institutions.

The revelation of January and February’s breaches by US officials comes amid strained ties between the two world powers.

US Defense Secretary James Mattis recently accused China of “intimidation and coercion” over its construction of military outposts on artificial islands in the South China Sea.

China condemned his comments as “irresponsible”.

Regarding Friday’s report, the Post said it had agreed to withhold some details about the compromised missile project at the request of the Navy, which said their release could harm national security.