One of Japan's biggest defence contractors, Mitsubishi Heavy Industries said today that it had been the victim of a cyber attack, the first publicly known attack targeting the country's defence industry.

The submarines, missiles and nuclear power plant components of the company are rumored to be the main targets of the intrusion, although Mitsubishi has yet to confirm exact details. A spokesperson for the defence contractor said that information could have been stolen but refused to further comment.

The Daily Yomiuri newspaper said approximately 80 computers were infected with viruses, including at least one Trojan horse, commonly used to steal information from its victim's computers.

The infected computers are at Mitsubishi Heavy Industries' headquarters in Tokyo, and more alarmingly, at manufacturing and R&D sites like Kobe shipyard where the giant builds submarines and nuclear power plant components.

Other affected company sites include Nagasaki shipyard, where escort ships are built for the Japanese Navy, and the Nagoya Guidance and Propulsion plant which makes guided missiles and rocket engines.

MHI is currently Japan's biggest defence contractor with around a quarter of the country's defence budget paid to them for their services in the last year. The company won 215 new contracts in this period worth 260 billion Yen ($3.4 billion).

Just last month, a Japanese defence white paper was released urging vigilance after numerous high-profile attacks this year against US defence contractors, including Lockheed Martin. At the time it was suggested that the attacks may have originated from China. MHI is currently investigating the intrusions and expects to release a press statement later today.