Japan's biggest defence contractor Mitsubishi Heavy Industries denied it lost critical data after malware was found riddled across computers in its war factories and offices.
The company detected up to eight different instances of malware including trojans and keyloggers in factories used to manufacture submarines, missiles and nuclear power plant components.
The company said in a statement (translated) leaked information may have included network data, and added that it was still investigating.
A Japan-based newspaper, Yomiuri, said 80 virus-infected computers were found at the company's Tokyo headquarters, manufacturing and research and development sites including its Nagoya Guidance & Propulsion System Works which manufactures rockets, and two shipyards which builds submarines components for nuclear power stations.
The malware was found in mid-August and reported to authorities.
The company said it had taken "measures to prevent the spread of damage" including the installation of anti-virus.
Reuters reported that Mitsubishi Heavy Industries bagged $3.3 billion worth of contracts from Japan's Ministry of Defence in the year to last March, or nearly a quarter of the ministry's spending that year.
Weapons included surface-to-air Patriot missiles and AIM-7 Sparrow air-to-air missiles.
Mitsubishi Heavy has also been working closely with Boeing, making wings for its 787 Dreamliner jets.