Information on Japan's Type 80 ASM-1 missile, which can be used against ships, may have been stolen during the August cyber attack on Mitsubishi Heavy Industries Ltd, the Yomiuri daily said on Wednesday.
Hackers accessed a server at a subcontractor to Mitsubishi Heavy 300,000 times from mid-August, and in one instance retrieved a large amount of data, the report said, citing unidentified sources close to the police investigation.
A portion of a report on the capabilities of the missile, used to provide air-launched coastal defenses against surface targets, may have been stolen, the Yomiuri said.
The report is classified as sensitive information but the data that may have been accessed is not seen as sensitive by the Defense Ministry, the paper said.
Mitsubishi Heavy, Japan's biggest weapons supplier, is investigating the August attack. A company spokeswoman said that so far it has not confirmed that information on its technologies has been accessed.
(Reporting by Mayumi Negishi; Editing by Edwina Gibbs)