横浜市（電子申請・届出システム／アララ株式会社のメール送信サービス）Data breach / unauthorized access incident
- Occurred on
- October 31, 2026
- Announced on
- November 3, 2026
- Severity
- BIncidents centered on names and contact details.
- Scale
- 820,000 accounts
- Main impact
- Usernames and email addresses for 約82万 registered accounts are subject to investigation, and suspension of the email delivery service has resulted in continued inability to register users or log in.
- Information involved
- Email addressFull name
- Cause / key point
- Unauthorized access caused by a third party exploiting a vulnerability in the web server in certain environments.About Exploitation of vulnerabilities
- Industry
- Government & municipal
- Listing / capital
- Government / public body
- Last updated
- November 4, 2026
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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: Exploitation of vulnerabilities(Breaking in through holes in software and devices)
Read the Exploitation of vulnerabilities guide and national trends →