YCC情報システム（山形市等）Data breach / unauthorized access incident
- Occurred on
- April 2, 2026
- Announced on
- May 20, 2026
- Severity
- AFinancial and HR records — information that easily translates into monetary damage.
- Scale
- Unknown
- Main impact
- There is a risk that the municipality's residents', tax, and insurance data were leaked. Some are said to include My Number and payroll information, but whether they were actually leaked is not specified.
- Information involved
- Identity verification data
- Cause / key point
- Intrusion using authentication credentials for a network device administrator account (estimated by an external specialist organization).About Abuse of credentials
- Industry
- Government & municipal
- Listing / capital
- Unlisted
YCC情報システム is unlisted.
- Last updated
- October 20, 2026
Is this incident worth paying attention to?
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: Abuse of credentials(Logging in legitimately with leaked or guessed passwords)
Read the Abuse of credentials guide and national trends →