SHINDO4

Mizuho Bank

Individual customersup to5,483people

POSSIBLE LEAKBank account / Phone numberLoss · Investigating

Open in the live monitor ▶
Disclosed
Feb 27, 2026
Leak
Leak possible
Type
Loss
Status
Investigating
Security spend
Not checked yet
Compensation
Not announced

What leaked

IdentityName or company name
ContactPhone number
Financial & paymentAccount number, Balance
Transactions & activityTransaction data such as remittances

How many

  • Individual customers up to 5,483 people
  • Corporate customers up to 43,054 organizations
  • Employees up to 9,601 people

Who is affected

  • Individual customers of overseas offices
  • Corporate customers
  • Employees

Cause

A storage medium from a dedicated test terminal at a sub-subcontractor for overseas system development is missing; possible unauthorized removal is being investigated

Timeline

  1. Security NEXT report date

Response

  • Forensic investigation

Investigating access logs and other records

What you should do

  1. Scammers who know your account number pose as refund staff. No bank or company asks for your PIN
  2. Treat refund or apology calls and texts as scams. Call back only on the number from the official site
  3. Expect targeted phishing posing as HR or interview contacts
  4. Check the company's notice to see if you're affected

Lessons for companies

  1. Put security requirements, audit rights and reporting deadlines in vendor contracts
  2. Don't keep ID or bank data: delete after checks or use a KYC provider
  3. Report to the PPC: preliminary in 3–5 days, final in 30 (60 if malicious)
  4. Run red teaming and AI-assisted hardening, and publish how much you invest

Sources