Mizuho Bank Discloses Loss of Storage Media at Subcontractor; Data of Over 48,000 Customers Potentially at Risk
Mizuho Bank announced that a storage medium containing sensitive customer information has been lost at one of its third-party system development subcontractors. The incident potentially affects nearly 60,000 individuals and corporate entities connected to the bank's overseas operations.
According to the bank’s disclosure, the missing media was part of a dedicated terminal used in a development environment for overseas systems. The loss occurred at a "secondary subcontractor" responsible for system development. While the bank is investigating the possibility of unauthorized removal, the storage device has not yet been located.
Scope of the Breach
The potential data exposure is significant, involving information from 18 locations across 11 countries and regions, including major financial hubs such as Hong Kong, Singapore, Seoul, and Sydney. The bank estimates the maximum number of affected parties to be:
- Corporate Customers: 43,054 companies
- Individual Customers: 5,483 persons
- Employees: 9,601 persons (current and former)
Nature of the Data
The missing data reportedly includes names, corporate titles, addresses, phone numbers, account numbers, balances, and transaction details. However, Mizuho stated that online banking credentials, such as IDs and passwords, were not contained on the lost media.
In a move to mitigate panic, the bank emphasized that the data is stored as raw character strings without discernible headers. "Deciphering the content would require highly specialized knowledge of the database structure and a specific environment, making it extremely difficult for a third party to view or understand the information," the bank stated.
Current Status and Response
Mizuho Bank confirmed that, as of the announcement, there has been no confirmed evidence of the data being misused by third parties. The bank apologized for the incident, citing its responsibility as a financial institution to strictly manage customer information, and pledged to prevent recurrence.
Inquiries regarding the incident are being handled by Mizuho’s transaction branches and a dedicated toll-free information line established for affected clients.
Norbert Gehrke
