Washington (CNN) Chinese government hackers have stolen large swaths of highly sensitive data on undersea warfare from a Navy contractor's computers, The Washington Post reports.

The stolen information includes secret plans to develop a supersonic anti-ship missile to be used by submarines by 2020, American officials told the Post.

The incidents took place in January and February, but officials did not disclose the contractor that was targeted, the newspaper reported Friday.

Although the information was highly sensitive, it was housed on the contractor's unclassified network, according to the Post.

"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," Navy Lt. Marycate Walsh said in a statement. "It would be inappropriate to discuss further details at this time."

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