Company

Mitsui Sumitomo Insurance Company, Limited

Mitsui Sumitomo Insurance Company, Limited (Chiyoda, Tokyo; Finance and insurance) appears in 2 related cybersecurity incidents. The latest was disclosed on 2025-11-27.

Profile

Industry/type: Finance and insurance
Location: Tokyo, Chiyoda
Website: https://www.ms-ins.com/

Public figures

Employees12,731Non-consolidated2026-03-31
METI: Gビズインフォ
Capital¥139.6BNon-consolidated2026-03-31
METI: Gビズインフォ

Metric	Value		As of	Source
Employees	12,731	Non-consolidated	2026-03-31	METI: Gビズインフォ
Capital	¥139.6B	Non-consolidated	2026-03-31	METI: Gビズインフォ

Incident history

Disclosed 2025-11-27Updated 2026-10-23Tokyo[Contained][Severity: Major][Through a supplier][Major]
Shin Nihon Kentei Kyokai: ransomware attack
[Ransomware][Data leak][Service outage]Leaked 30KOrganizations 5
Disclosed 2024-10-07Updated 2026-10-23Tokyo[Contained][Severity: Critical][Through a supplier][Critical]
Tokyo Sonpo Kantei: ransomware puts customer data of several insurers at risk
[Ransomware][Credential abuse][Data leak][Extortion]Leaked 120KOrganizations 6

		Incident	Role	Impact level				Methods	Impacts		Status
2025-11-27	2026-10-23	Shin Nihon Kentei Kyokai: ransomware attack	[Through a supplier]	[Major]	[Major]	5 Aioi Nissay Dowa Insurance Co., Ltd., Mitsui Sumitomo Insurance Company, Limited, Sompo Japan Insurance Inc., Tokio Marine & Nichido Fire Insurance Co., Ltd., Shin Nihon Kentei Kyokai	Tokyo	[Ransomware]	[Data leak][Service outage]	30,000	[Contained]
2024-10-07	2026-10-23	Tokyo Sonpo Kantei: ransomware puts customer data of several insurers at risk	[Through a supplier]	[Critical]	[Critical]	6 Mitsui Sumitomo Insurance Company, Limited, Tokyo Sonpo Kantei Inc., AIG General Insurance Company, Ltd., Sompo Japan Insurance Inc., Tokio Marine & Nichido Fire Insurance Co., Ltd., Nisshin Fire & Marine Insurance Co., Ltd.	Tokyo	[Ransomware][Credential abuse]	[Data leak][Extortion]	120,000	[Contained]