Police have arrested a 41-year-old man on suspicion of leaking personal information on 24,600 customers of NTT DoCoMo Inc., police officials said Thursday.

Police arrested Yoshitaka Takemura, a contract employee at an NTT DoCoMo affiliate, on suspicion of obstructing the business of the mobile phone operator.

According to police, Takemura obtained mobile phone numbers and other personal data on the company's subscribers earlier this year and sent a threatening e-mail to NTT DoCoMo Systems Inc., an NTT DoCoMo affiliate.

The e-mail said, "Data of your precious clients have been leaked. I will distribute several tens of thousands of data if you do not immediately launch an in-house investigation, hold a news conference to apologize and send out a press release on the incident."

The leaked information came from partial lists of DoCoMo subscribers in Niigata Prefecture and neighboring areas, including names, addresses, mobile phone numbers and phone numbers used for inquiries, DoCoMo said earlier.

Takemura obstructed the business of the two firms by sending them 310 items of personal data in the e-mail, prompting them to hold a crisis meeting, police said.

Takemura reportedly told police he leaked the data to teach the company about a loophole in the system.