Tokyo Gas says personal information on more than 4 million people may have been leaked outside. The major Japanese utility says it has not confirmed illicit usage of the data.

The company says it confirmed on June 26 that the network of a subsidiary had suffered unauthorized access. The subsidiary sells infrastructure management systems to gas and water supply operators.

Tokyo Gas notes that an investigation by an outside expert organization has found that personal information on about 4.16 million people, which is stored in the servers of Tokyo Gas and the subsidiary, might have been leaked.

It says the information include the names, addresses and contact details of customers that were provided by client firms, but does not have bank account or credit card information.

Tokyo Gas adds that personal data on about 3,000 employees of the subsidiary may also have been leaked, and some bank account information is included.

The company says it offers a deep apology and will continue with its efforts to determine the cause and prevent a recurrence.