Chinese government hackers breached the computer system of a Navy contractor and stole large amounts of sensitive data, The Washington Post reports.

The Post said the hacking took place in January and February, according to U.S. officials speaking on the condition of anonymity.

It said the stolen information amounted to 614 gigabytes of material, including secret plans to develop a supersonic anti-ship missile for use on U.S. submarines by 2020.

Other information stolen included signal and sensor data for submarines, information relating to cryptographic systems, and a Navy electronic warfare library. The Post said details on hundreds of mechanical and software systems were compromised in the hacking.

The paper said the data was highly sensitive despite being on a contractor’s unclassified computer network. It said U.S. officials did not identify the contractor, but said he worked for the Naval Undersea Warfare Center, a U.S. military organization headquartered in Newport, Rhode Island.

The Navy is investigating the breach along with the Federal Bureau of Investigation, according to the Post. Investigators told the paper the hack was carried out by the Chinese Ministry of State Security, a civilian spy agency.

U.S. officials believe China has for years carried out hacking attacks on the U.S. military, the U.S. government and U.S. companies.

China has recently made it a priority to increase its development of undersea warfare to diminish the gap in the U.S. superiority in this area.
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