SHINDO4

TAC

TAC Co., Ltd.

Personal dataup to1,315people

LEAK CONFIRMEDPostal address / Full nameMisconfiguration · Closed (final report)

Open in the live monitor ▶
Disclosed
Dec 22, 2025
Detected
Nov 2025
Detection to disclosure
51 days
Leak
Leak confirmed
Type
Misconfiguration
Status
Closed (final report)
Security spend
Not checked yet
Compensation
Not announced

What leaked

IdentityFull name
Account dataMember number
Transactions & activityStudy location, instructor, courses, subjects passed and results history, Exam venue and exam number
ContactAddress

How many

  • Candidates in the 2013 tax accountant exam up to 1,315 people
  • Including home address 351 people

Who is affected

  • Students (tax accountant exam candidates)

Cause

A work error that temporarily deviated from the normal workflow left a file containing personal data unintentionally published on the internet

Timeline

  1. Late July 2014
  2. Mid-November 2025
  3. A candidate found their own data through a search engine and contacted the company
  4. Date of the Security NEXT report

Response

  • Data deleted

What you should do

  1. Watch for unexpected mail or invoices; your address is hard to change
  2. Check the company's notice to see if you're affected

Lessons for companies

  1. Two-person review and pre-release tests for sharing and cache changes; monitor cloud config (CSPM)
  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