TOPPAN（損保ジャパン）Data breach / unauthorized access incident
- Occurred on
- September 1, 2026
- Announced on
- September 29, 2026
- Severity
- CLimited data such as email addresses and identifiers.
- Scale
- 177,426 people
- Main impact
- Kana names and policy numbers, etc. for 177,426 individuals (possible duplicates) were mistakenly sent to one other non-life insurer, but complete deletion by the recipient has been confirmed. Email addresses, postal addresses, bank account information, etc. were not included.
- Information involved
- Email addressCard & payment dataHome addressFull name
- Cause / key point
- Erroneous manual operation by contractor TOPPAN and inadequate verification procedures.About Supply chain attacks (via vendors & shared services)
- Industry
- Finance & insurance
- Listing / capital
- Listed company東証プライム 7911(TOPPANホールディングス)
- Sources
- Last updated
- October 20, 2026
Stock price reaction to the disclosureTOPPANホールディングス / 東証プライム 7911
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Written & reviewed
Reviewed byYutaro SasaoFounder & CEO, MediaLeap Inc.
CEO of MediaLeap Inc. Working on both sides of web advertising and web media since 2013; founded the company in May 2025.
Review scope: cross-checking against primary sources (official and government announcements), verifying claims stay within the facts, and checking source attribution。Last reviewed:
Written by:Leak Watch editorial team (AI-assisted drafts verified against sources by the editorial team) · Reviewer profile · Request a correction
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Attack method classification: Supply chain attacks (via vendors & shared services)(Compromising the provider instead of the user)
Read the Supply chain attacks (via vendors & shared services) guide and national trends →