---
title: "Mitsui Sumitomo Insurance MS Compass data incident"
description: "Mitsui Sumitomo Insurance confirmed leakage of approximately 23,000 MS Compass customer records."
incident_type: "Cybersecurity incident"
status: "active"
last_modified: "2026-11-09"
canonical_url: "https://www.ally.security/incidents/mitsui-sumitomo-ms-compass-data-incident-2026"
markdown_url: "https://www.ally.security/incidents/mitsui-sumitomo-ms-compass-data-incident-2026.md"
stix_url: "https://www.ally.security/incidents/mitsui-sumitomo-ms-compass-data-incident-2026/stix.json"
---

# Mitsui Sumitomo Insurance MS Compass data incident

Unauthorized access affected the insurer’s MS Compass business-information site, which was temporarily closed.

Last modified Nov 9, 2026 · 1 source

## Summary

- **Environment:** MS Compass business-information site
- **Operational impact:** Access restrictions followed by full temporary site closure
- **Financial impact:** No incident cost disclosed

## What happened

[Mitsui Sumitomo Insurance](https://www.ms-ins.com/) detected unauthorized access to MS Compass on November 2–3, 2026 and subsequently confirmed a data leak. [1](#source-1)

## Impact

- Approximately **23,000 records** were affected: registered members, seminar applicants from November 2023 through November 2026, and inquiry-form users. [1](#source-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](#source-1)

## Timeline

### November 3, 2026 — Access restrictions applied

Mitsui restricted parts of the system. [1](#source-1)

### November 6, 2026 — Entire site temporarily closed

MS Compass was taken offline. [1](#source-1)

### November 9, 2026 — Data leak disclosed

The [MS Compass notice](https://www.ms-ins.com/news/fy2026/pdf/1109_2.pdf) details the affected population. [1](#source-1)

### November 9, 2026 — 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](#source-1)

## Assets

[Download the case-scoped STIX 2.1 bundle](<https://www.ally.security/incidents/mitsui-sumitomo-ms-compass-data-incident-2026/stix.json>)

## Sources

Primary source records used to research this incident.

<a id="source-1"></a>

### Mitsui Sumitomo Insurance MS Compass information-leakage notice

official · Mitsui Sumitomo Insurance · Nov 9, 2026

<https://www.ms-ins.com/news/fy2026/pdf/1109_2.pdf>

<details>
<summary>Evidence ledger</summary>

Review the supporting structured claims.

1. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: MS Compass site temporarily closed
2. **Occurred At · 100% confidence · current**  
   MS Compass site temporarily closed: 2026-11-06
3. **Disclosed At · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: 2026-11-09
4. **Affected Organization · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Mitsui Sumitomo Insurance
5. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Approximately 23,000 records were affected as of November 9. The population includes registered members, customers who applied for company seminars from November 2023 through November 2026, and inquiry-form users.
6. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Affected fields included company names and identifiers, job titles, names, email addresses, phone numbers, industry, business addresses, revenue and employee counts. Credit-card and bank-account information were excluded.
7. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: External specialists were investigating cause and scope. Individual notifications were planned; the company had not confirmed misuse of the leaked data as of November 9.
8. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: MS Compass data leak disclosed
9. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Mitsui restricted some system access on November 3 and temporarily closed the entire site on November 6. It reported no external unauthorized access after November 3.
10. **Occurred At · 100% confidence · current**  
   Access restrictions applied: 2026-11-03
11. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Mitsui Sumitomo Insurance detected unauthorized access to its MS Compass business-information site on November 2–3, 2026 and confirmed customer-information leakage.
12. **Resulted In · 100% confidence · current**  
   Mitsui Sumitomo Insurance MS Compass data breach: Access restrictions applied
13. **Occurred At · 100% confidence · current**  
   MS Compass data leak disclosed: 2026-11-09

</details>