Sansan（Sansan User Forum）Data breach / unauthorized access incident
- Occurred on
- Unconfirmed
- Announced on
- October 9, 2026
- Severity
- AFinancial and HR records — information that easily translates into monetary damage.
- Scale
- 8,687 people
- Main impact
- Confirmed leakage of emails, profiles, etc. of 1,325 members. In addition, profiles, etc. of another group of 8,687 members are at risk of leakage, and the community has been suspended.
- Information involved
- Email addressUser / member ID
- Cause / key point
- Unauthorized access to contractor Commune.About Supply chain attacks (via vendors & shared services)
- Industry
- IT & telecom
- Listing / capital
- Listed company東証プライム 4443(Sansan)
- Last updated
- October 20, 2026
Stock price reaction to the disclosureSansan / 東証プライム 4443
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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 →