Skip to content
Mitsui Sumitomo Insurance
Tokyo, Japan2 sources
Confirmed:Confirmed by the organisation, a regulator or a securities filing. First reported 4 Nov 2026.
Japanese insurers disclose breach of 480,000 personal records
Mitsui Sumitomo Insurance and Aioi Nissay Dowa Insurance in Japan disclosed unauthorized access to a policyholder website exposing approximately 480,000 personal records. The data included names, addresses and telephone numbers.
- Type
- Data breach
- Sector
- Finance
- Records
- 480K records confirmed
- First reported
- 4 Nov 2026
- Latest source
- 6 Nov 2026
What to do
- If you have an account, change that password, and anywhere you reused it.
- Turn on two-factor authentication, ideally an authenticator app or passkey, not SMS.
- Expect phishing that uses your real details. Do not click links in messages about this incident; go to the company's site directly.
- If payment cards were involved, watch statements and ask your bank for a new card.
- If government ID or social security numbers were involved, consider a credit freeze.
- If this is a vendor of yours, ask what of your data they held and whether it was in scope.
- Reset any API keys, SSO trusts or shared credentials you have with them.
- Brief your help desk: attackers often impersonate the breached brand next.
Not sure? Ask an assistant with the sources attached, or have a coding agent check your systems.
Check your systems for Mitsui Sumitomo Insurance
Sources
2- news.web.nhk6 Nov 2026news.web.nhk/newsweb/na/nd-20261106de71530
- cybersecurity-jp.com4 Nov 2026cybersecurity-jp.com/news/118127
Confidence 80% that this is real and correctly placed. Locations are city centroids at best. Spotted an error? Report a correction.