Japanese mobile phone operator NTT DoCoMo says it has implemented new stringent security measures following the theft of around 24,600 personal customer data records from a secure room at its facility in Tokyo.
DoCoMo admitted in February that the personal data of some mobile phone subscribers had been leaked.
According to Japanese press reports, ex-DoCoMo employee Yoshitaka Takemura, 41, was arrested by the Metropolitan Police Department in Tokyo last week in connection with the theft of DoCoMo client data.
Takemura allegedly copied the customer data, including names, addresses and phone numbers, to a portable memory device. The information was copied from a computer in a 'security room' at the telco's facility in Minato Ward, Tokyo, while he was working at the firm in January. He then reportedly sent 311 e-mails containing the stolen data to DoCoMo subscribers.
In a statement DoCoMo says president and CEO Masao Nakamura and senior executive vice president, Kunio Ishikawa, will both be penalised for the incident, along with "an employee".
DoCoMo says it conducted an internal investigation following the leak and cooperated with the Tokyo Metropolitan Police Department's investigation.
The new security measures include improved monitoring of the security room, with more cameras installed and a restriction on the number of staff allowed access. The firm has also pledged to implement an enterprise-wide programme to educate staff on data protection and security laws. Areas of the business that handle personal data will also be examined and inspected regularly.
News of the data leak is particularly embarrassing for DoCoMo as it follows yesterday's announcement that the company is expanding further into financial services by acquiring a stake in Sumitomo Mitsui Cards.