NTT Docomo says a cyberattack exposed customer information linked to as many as 294,839 mobile lines, including records from its Docomo Online Shop and My docomo services. The company disclosed the updated figure at a November 6 press conference, after its latest incident notice listed the impact as up to about 300,000 records.
The total comprises 204,157 individual customer lines and 90,682 corporate lines, according to reporting by TECH+ and Impress Watch. The count also includes information belonging to some customers who had already canceled their service.
The exposed information included names, dates of birth, ages, addresses, phone numbers, email addresses, identity-document numbers, mobile subscription details, contract start dates, rate plans, options and discounts. For some customers, the records also contained information about legal or procedural representatives, employers and companies, as well as bank names, branch details, account numbers and account holders.
Docomo said the attackers accessed its systems over the internet and abused links between multiple systems to search for and retrieve customer information automatically. The company said the attack did not directly target an API but used existing functions in an unexpected combination. It first detected unusually high access on November 4. After blocking overseas IP addresses and temporarily placing My docomo into maintenance, the company restored the service, but detected suspicious activity again later that night. It moved both services into emergency maintenance at 1:05 a.m. on November 5 and confirmed the data leak at 2:10 a.m.
The company said it has blocked the identified attack route and similar paths. It also suspended new registrations through its ahamo mobile-plan website on November 6 as a precaution, although it said it had not detected unauthorized access to that site. Docomo Online Shop and My docomo remain under emergency maintenance, with no restoration date announced. The company is considering compensation for affected individual and corporate customers but has not decided the terms or amounts.
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