ブックオフグループ(ブックオフコーポレーション)Data breach / unauthorized access incident
- Occurred on
- October 4, 2026
- Announced on
- October 9, 2026
- Severity
- SCompromise of deep personal data or usable credentials.
- Scale
- 6,383,279 people
- Main impact
- Due to unauthorized access to the membership management system, personal data for 6,383,279 individuals (6,427,735 membership records), including names, dates of birth, addresses, phone numbers, email addresses, and password hashes, including approximately 210,000 former members, were transmitted externally (confirmed in the second report on October 13).
- Information involved
- Email addressUser / member IDPasswordPhone numberHome addressFull nameDate of birth
- Cause / key point
- Between October 4 and 6, unauthorized third-party access to the membership management system occurred and data was transmitted externally.
- Industry
- Retail & e-commerce
- Listing / capital
- Listed company東証プライム 9278(ブックオフグループホールディングス)
- Sources
- Last updated
- October 20, 2026
Stock price reaction to the disclosureブックオフグループホールディングス / 東証プライム 9278
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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: Unauthorized access (method undisclosed)(Breached, but the technique was not identified or disclosed)
Read the Unauthorized access (method undisclosed) guide and national trends →