Sensitive data including plans for nuclear power plants and fighter jets "apparently was stolen" from Japanese industrial manufacturer Mitsubishi Heavy Industries (MHI) during the cyber attack it uncovered in August 2011.

When the company revealed the attack in September, it said ""crucial data about our products or technologies have been kept safe". But the Asahi Shimbun newspaper this week cited ‘sources’ as saying that since then, an internal investigation found evidence that nuclear and military data was in fact taken during the attack.

A company spokesperson contacted by the paper declined to commenti on whether sensitive data had in fact been stolen.

MHI reported the incident to the police in September. It said that 83 computers at various locations had been infected with eight viruses. However, Japanese newspapers reported earlier this month that the computers were in fact infected with at least 50 different kinds of virus.

This is not the first time a member of the Mitsubishi group of companies has leaked nuclear secrets as a result of malware infection. In 2005, a virus on a Mitsubishi Electric employee’s home PC automatically uploaded plans of cooling systems for nuclear power plants to a peer-to-peer file-sharing service.

Asahi Shimbun also reported that a cyber attack "mounted from a server in China" stole log-in details for a government network from the PCs of three politicians in Japan’s House of Representatives.