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JAENES
BPossible leakOctober 19, 2026 announced

Z会（Z-ID）Data breach / unauthorized access incident

笹尾 祐太朗の写真Reviewed by Yutaro SasaoWritten by Leak Watch editorial team published ・ updated
Occurred on
October 15, 2026
Announced on
October 19, 2026
Severity
BIncidents centered on names and contact details.
Scale
13 accounts
Main impact
In the Z会グループ Z-ID system, 13 instances of password reset operations by a third party (rapid consecutive password changes) were confirmed in the early hours of 2026-10-15. The "氏名", "メールアドレス" and "Z-ID" of the 13 affected accounts may have been exposed; there is no evidence of direct unauthorized intrusion into servers or databases or of a cyberattack, and no misuse or secondary damage has been confirmed. Affected accounts were suspended and contacted individually, and the password reset function was temporarily disabled and later reinstated after security enhancements.
Information involved
Full nameEmail addressUser / member ID
Cause / key point
Unauthorized access to the Z-ID system by a third party (unauthorized password reset operations)About Abuse of credentials
Industry
Education
Listing / capital
UnlistedParent company: 株式会社増進会ホールディングス
Sources
Last updated
October 23, 2026

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Written & reviewed

笹尾 祐太朗の写真

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: Abuse of credentials(Logging in legitimately with leaked or guessed passwords)

Read the Abuse of credentials guide and national trends →

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