High-speed Internet access provider ACCA Networks Co. said Thursday that personal data on 339,177 customers has been leaked.
The information includes names, mail addresses, telephone numbers and e-mail addresses.
The figure includes the data leaked from 201 ACCA customer files, details of which were announced in March, it added.
At a news conference the same day, ACCA President Yoshio Sakata apologized.
"We've caused customers so much trouble," he said.