The telecommunications ministry will issue a warning this week to the Softbank Corp. group over a massive leak of client data from Internet service provider Softbank BB Corp., ministry officials said Monday.

The Public Management, Home Affairs, Posts and Telecommunications Ministry will summon Softbank President Masayoshi Son to give him an administrative directive, they said.

In the warning, the ministry will express regret that the group failed to meet directives the ministry issued earlier for the Internet and telecom industries to maintain the security of private client information. It will also call for preventing a recurrence of any data leak, the officials said.

The leak came to light in January when the group admitted it had detected signs that private information of people who subscribed to Softbank BB’s Yahoo BB asymmetric digital subscriber line services had been leaked last year. The leak involved information on 4.51 million subscribers.

Pointing out that there were a number of outside people who could gain access to Softbank BB’s client database, critics said the group’s information security system was lax.

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