TOKYO: Mitsubishi Electric Corp. said Monday that its internal computer networks were hit by a cyberattack and that personal information of its employees and confidential corporate information may have been compromised.

But the Japanese electronics maker said that its internal investigation found no breaches of secret information related to the defense sector and such social infrastructure as electricity and railway systems.

The cyberattack came to light after Mitsubishi Electric detected irregular activity on a device at the company on June 28 last year.

Having found that computers at the company and its computer servers had been hacked, Mitsubishi Electric promptly took measures to limit outside access to its internal networks, the company said.

Unauthorized accesses hit multiple business divisions at the company. The tactics used were very sophisticated, designed to leave no evidence of invasion, according to Mitsubishi Electric.

A Chinese-affiliated hacker group that targets defense-related secret information may have been involved in the attack, sources familiar with the situation said.

The attack also targeted Mitsubishi Electric's business partners, including government ministries and agencies such as the Defense Ministry and the Nuclear Regulation Authority, and private-sector companies in the power generation, telecommunications, railway and automobile industries.

The information that may have been compromised includes documents about Mitsubishi Electric's internal meetings, as well as data on its technologies and the personal information of employees.

The company said in a statement that it has confirmed there was no damage from the attack.

Mitsubishi Electric apologized for causing concerns among people concerned and its clients.

Chief Cabinet Secretary Yoshihide Suga, Japan's top government spokesman, told a press conference on Monday that the government has received a report from Mitsubishi Electric about the unauthorized accesses.

The government has confirmed there were no breaches of secret information about defense equipment and electricity infrastructure, he said.

JIJI Press