Japan is under pressure to bolster cyber security after an attack on Mitsubishi Heavy Industries may have netted military data.
The attach on Japan's biggest defence contractor could have gained military data on warplanes and information on nuclear power plants, Japan newspaper the Asahi newspaper reported this week.
However it remains unclear whether the military data from Mitsubishi Heavy, including information on warplanes, helicopters and other equipment ordered by Japan's Defence Ministry, is deemed sensitive defence information, the Asahi said, citing a source close to the matter.
A Japanese defence ministry official said the ministry was not aware of any leaks of information classified as defence secrets, while Mitsubishi Heavy spokesman Hideo Ikuno declined to comment on the matter.
Mitsubishi Heavy, Japan's biggest weapons supplier, said last month that network information such as IP addresses may have leaked but that it had so far not confirmed any leaks of data on its products or technologies.
More than 80 computers or servers were found to have been infected by viruses, and checks on dozens of other servers in Japan showed that there were indications of leaks of military and nuclear power plant data, the Asahi reported.
It is highly likely that someone went in to steal the data, Asahi said, citing the source.
Mitsubishi Heavy, a partner with Boeing in weapons production, delayed reporting the incident, which became publicly known in August, in a possible violation of its military supply contracts.
Rivals IHI Corp and Kawasaki Heavy Industries have also said they have received suspicious e-mails, while a contractor to Mitsubishi Heavy is checking whether there had been a breach of sensitive data.
Japan is moving to strengthen its cyber security in line with calls from Washington, and will set up a framework for sharing hacking information among governmental and private institutions, the Nikkei business daily reported this week.
Mitsubishi Heavy, IHI and Kawasaki Heavy Industries, as well as Toshiba, Hitachi, Fujitsu, NEC and others, will take part in the framework, the Nikkei said, without citing sources.