A cyber attack on Japan's largest arms contractor targeted about 80 servers and computers at 11 facilities related to nuclear power, missiles and submarines.
The Defence Minister, Yasuo Ichikawa, said yesterday that no sensitive data was known to have been stolen in the attack on Mitsubishi Heavy Industries.
He said that he had instructed the company to strengthen its data security systems.
The attack was discovered last month, but the government only found out about it from press reports on Monday.
The company said it was working with police and independent experts to investigate the attack. It said there was no confirmed leak of sensitive data involving its products or technology.
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