SHINDO5

Seicomart

Seicomart Company, Ltd.

online.seicomart.co.jp

App members (approx. 49%)572,022people

LEAK CONFIRMEDDate of birth / Postal addressUnauthorized access · Investigating

Open in the live monitor ▶
Disclosed
Sep 29, 2026
Detected
Sep 28, 2026 17:00 JST
Detection to disclosure
1 day
Leak
Leak confirmed
Type
Unauthorized access
Status
Investigating
Security spend
Measures, no amount
Compensation
Compensation offered
Corporate number
6430001075018

What leaked

IdentityFull name, Gender, Date of birth
ContactAddress, Phone number, Email address
Account dataClub Card enrollment date, Membership cancellation date

How many

  • App members (approx. 49%) 572,022 people

Who is affected

  • Members

Cause

Unauthorized access to the server of the "Seicomart App" (details withheld because of cooperation with the police)

Timeline

  1. Intrusion began
  2. Intrusion stopped
  3. Detected
  4. Server connections shut down
  5. Service suspended
  6. First disclosure
  7. Company issued an update
  8. Company issued an update
  9. Company issued an update

Response

  • Forensic investigation
  • Hotline
  • Phishing warning
  • Service stopped

Investigation by an outside investigation firm, suspension of member-related functions, warnings about spoofed emails, inquiry helpline set up

What you should do

  1. Don't open links in emails from this company. The apology email itself may be fake
  2. Treat refund or apology calls and texts as scams. Call back only on the number from the official site
  3. Watch for unexpected mail or invoices; your address is hard to change
  4. Check the company's notice to see if you're affected

Lessons for companies

  1. Patch internet-facing servers, VPNs and admin panels first. Exploits follow disclosure within days
  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