Summary
- Environment: MS Compass business-information site
- Operational impact: Access restrictions followed by full temporary site closure
- Financial impact: No incident cost disclosed
- Record status: Developing record. Reviewed November 9, 2026; updated as evidence emerges.
What happened
Mitsui Sumitomo Insurance detected unauthorized access to MS Compass on November 2–3, 2026 and subsequently confirmed a data leak. [1]
Impact
- Approximately 23,000 records were affected: registered members, seminar applicants from November 2023 through November 2026, and inquiry-form users. [1]
- Fields included company and contact details, job titles, business identifiers, industry, addresses, revenue and employee counts. Card and bank-account information were excluded. [1]
Timeline
Access restrictions applied
Mitsui restricted parts of the system.
[1]Entire site temporarily closed
MS Compass was taken offline.
[1]Data leak disclosed
The MS Compass notice details the affected population.
[1]Briefing updated
This briefing was last reviewed and updated on November 9, 2026.
Threat Group & Attack Vector
The initial access method has not been disclosed.
Actors
- No threat actor group has been identified in the reviewed public evidence.
TTPs
- No specific MITRE ATT&CK technique is currently mapped for this case.
Response
Mitsui reported no external unauthorized access after November 3. Outside specialists were investigating, individual notifications were planned, and no data misuse had been confirmed by November 9. [1]