SHINDO3

Mizuho Bank

Mizuho Bank, Ltd.

iDeCo online applicants5,572people

LEAK CONFIRMEDEmail address / Contract detailsMisdelivery · Closed (final report)

Open in the live monitor ▶
Disclosed
Jun 16, 2025
Leak
Leak confirmed
Type
Misdelivery
Status
Closed (final report)
Security spend
Not checked yet
Compensation
Not announced

What leaked

ContactEmail address
Transactions & activityApplication receipt number
Account dataApplication status

How many

  • iDeCo online applicants 5,572 people

Who is affected

  • Online applicants for iDeCo (individual-type defined contribution pension)

Cause

A file was sent by email to the wrong partner financial institution

Timeline

  1. Exposure began
  2. Date of the Security NEXT report

Response

  • Data deleted

Confirmed that the recipient deleted the email and file

What you should do

  1. Don't open links in emails from this company. The apology email itself may be fake
  2. Check the company's notice to see if you're affected

Lessons for companies

  1. Use DLP: recipient checks, send delay, automatic attachment protection
  2. Report to the PPC: preliminary in 3–5 days, final in 30 (60 if malicious)
  3. Run red teaming and AI-assisted hardening, and publish how much you invest

Sources