Mitsui Sumitomo Insurance portal breach leaks about 37,000 customer records
Unauthorised access to Japanese insurer Mitsui Sumitomo Insurance’s policyholder portal resulted in the leak of approximately 37,000 customer records. The leaked information included insurance policy numbers, names, addresses, telephone numbers and email addresses, but did not include credit card or bank account information. The company suspended the related services and conducted an external forensic investigation.
Key facts
- Affected organisation
- Mitsui Sumitomo Insurance
- Incident type
- Data breach
- Occurred / detected
- Not confirmed
- Scale of damage
- Approximately 37,000 customer records
- Cause / method
- Unauthorised access to the policyholder portal
- Location
- Japan
If your data was exposed
Exposed dataNameAddressPhone numberEmail
- Don’t tap links in texts, calls or emails that mention this incident and offer compensation, refunds or breach checks. Check directly on the organisation’s official website or app.
Timeline
- The leak of approximately 37,000 customer records following unauthorised access to the policyholder portal, the suspension of related services and an external forensic investigation were confirmed.
6 related reports
- Mitsui Sumitomo Insurance Policyholder Page: Unauthorized Access Confirms Leak of Approximately 37,000 Records – Am I Affected? Policy Numbers, Names, Addresses, Phone Numbers, and Email Addresses (As of November 6, 2026, 9:00 AM)
- ドトールコーヒー（ドトールオンラインショップ） data breach / unauthorized access incident (November 6, 2026)
- 日本ネットワークセキュリティ協会（JNSA） data breach / unauthorized access incident (November 6, 2026)
- Security incident disclosure — November 2026
- Mitsui Sumitomo Insurance confirms Policyholder Page leak of about 37,000 records
- 当社システムへの不正アクセスに伴う情報漏えいについて
Other incidents at Mitsui Sumitomo Insurance
Mitsui Sumitomo Insurance’s MS Compass leaks around 23,000 customer records
23kImpact: Around 23,000 records belonging to members, seminar applicants and people who submitted enquiries
Unauthorised access to Mitsui Sumitomo Insurance’s corporate information website MS Compass exposed around 23,000 records belonging to members, seminar applicants and people who submitted enquiries. The records included company names, contact names, email addresses, telephone numbers and addresses. The website was temporarily closed.
Related reports: 3 →Supplier breach exposes 228,000 Mitsui Sumitomo Insurance customer records
228kImpact: Approximately 228,000 motor insurance customer records
Unauthorised access to Prestige Core Solution, Mitsui Sumitomo Insurance’s roadside assistance contractor, exposed approximately 228,000 motor insurance customer records. The leaked information included names, addresses, phone numbers, vehicle information, and records of accident and breakdown reports. This incident is separate from the MS Compass breach.
Related reports: 2 →
The summary and key facts are written by AI from related reports and may contain errors. Check the original articles and the organisation’s official statements for accurate details.