Key takeaways

  • TOPPAN (TOPPAN株式会社), the Japanese printing and business services group, said on September 29, 2026 that it had sent data on 177,426 Sompo Japan policyholders to another non-life insurer by mistake.
  • TOPPAN runs a shared service that issues insurance premium deduction certificates, used for tax purposes, for 14 insurers. An operator dragged and dropped the wrong ZIP file while sending data to the insurers by hand.
  • The data included names in katakana, policy numbers and an internal ID. No addresses, dates of birth, contact details or financial data were included. The receiving insurer deleted it.
  • TOPPAN's recurrence measures rely mainly on a second person checking the work. Automating the process is described as a permanent fix, with no date.

What happened#

TOPPAN operates the "insurance premium deduction certificate issuance service" (保険料控除証明書発行サービス). According to Sompo Japan, the service was built by six non-life insurers, the General Insurance Association of Japan (GIAJ) and TOPPAN. Fourteen insurers now outsource its operation to TOPPAN.

According to TOPPAN's notice:

Date (2026) Event
Sep 1 While sending list data to insurers by hand, an operator drags and drops Sompo Japan's ZIP file into the ZIP file meant for another insurer. The files are sent without rechecking what is inside
Sep 1, 17:15 The receiving insurer asks GIAJ about another company's policyholder data in its file
Sep 2 GIAJ asks TOPPAN to investigate. TOPPAN stops deliveries through the file transfer service it used
Sep 29 TOPPAN and Sompo Japan announce the incident

The list was a CSV file of policyholders who no longer need a paper postcard certificate. Several insurers' ZIP files were in the same folder. The drag-and-drop copied Sompo Japan's ZIP into the other insurer's ZIP, and nobody checked the contents before sending.

TOPPAN says the cause was a manual error and a gap in its checking procedure, not a system failure or a cyberattack. It found no other case of one insurer's data being mixed into another's.

What was exposed#

Data Status
Name in katakana Sent to another insurer
Policy number used for tax deduction certificates Sent to another insurer
Business ID (certificate year, insurer code and policy number combined) Sent to another insurer
Name in kanji, address, date of birth, phone, email Not included
Credit card, bank account, My Number Not included

The count of 177,426 may include the same person more than once, so the real number may fall. Both companies say the receiving insurer deleted the data completely, and no further leak or misuse has been found. Sompo Japan is notifying affected policyholders by email, or by letter if no email address is registered.

Neither company has named the insurer that received the data.

TOPPAN's recurrence measures#

TOPPAN lists four measures:

  1. Attach files using the "choose file" dialog only, instead of drag-and-drop.
  2. Put a checker separate from the operator to review the whole process.
  3. Compare the size and timestamp of attached files with the original data.
  4. As a permanent measure, systemize the sending process to reduce the risk of manual work.

What we don't know yet#

TOPPAN and Sompo Japan have not said:

  • When the sending process will be automated, and what happens until then
  • Whether the other 13 insurers' data goes through the same manual process
  • Whether the incident was reported to the Personal Information Protection Commission. Neither notice mentions it
  • Why it took four weeks from the recipient's report to public disclosure

Our analysis#

The error was invisible, so a second person may miss it too#

A two-person check, often called a "double check" (ダブルチェック) in Japan, is one of the most common recurrence measures in Japanese notices about misdirected mail and email. It works when the mistake is visible: a wrong address, a wrong file name, a wrong attachment.

This mistake was not visible. The file names were right. The wrong data was inside a ZIP file that had been altered in its folder before it was sent. A checker looking at the same screen would most likely have seen the same correct-looking file.

TOPPAN seems to recognize this, because its third measure compares file size and timestamp with the original data. That helps only if the "original" is something the error cannot touch. In this case, the ZIP file in the folder was the thing that changed. The notice does not say what the attached file will be compared against.

Automation is the real fix, and it has no date#

TOPPAN deserves credit for naming systemization as the permanent measure. A process that generates each insurer's file and sends it without a person moving files around removes this kind of error entirely.

But the notice gives no date, and the timing matters. In Japan, insurers send premium deduction certificates in the autumn, ahead of the year-end tax adjustment (年末調整). That is when a service like this is at its busiest. Until the process is automated, it depends on people moving files by hand, with a second person watching.

One vendor, one folder, fourteen insurers#

The service is shared. One vendor handles data for 14 competing insurers, and in this case, several insurers' files sat in the same folder. Shared services save cost, but they also put many companies' data one mistake away from each other. For the insurers, this is a third-party risk question as much as a TOPPAN one. Sompo Japan says it will strengthen its oversight of contractors. The other insurers using the service have not said anything publicly.

The recipient did the right thing#

The mistake was found the same day because the receiving insurer noticed data that was not its own and reported it, through the industry association, instead of quietly deleting it. TOPPAN's own checks did not catch it. The data involved was limited, and it went to a regulated company that deleted it. It could have been much worse.

What this means for readers#

  • If you are a Sompo Japan policyholder, watch for a notice by email or letter. The data sent did not include your address, contact details or financial information.
  • Be wary of messages that mention this incident and ask for personal or payment details. Sompo Japan's dedicated line for this case is 0120-175-675 (weekdays 9:00–17:00, Japan time).
  • If your organization shares a vendor with its competitors, ask how the vendor keeps each client's data apart when people handle files by hand.

Japanese terms at a glance#

Japanese Reading Meaning
誤送付 gosōfu Sending something to the wrong recipient
保険料控除証明書 hokenryō kōjo shōmeisho Insurance premium deduction certificate, used for tax
年末調整 nenmatsu chōsei Year-end tax adjustment by employers
ダブルチェック daburu chekku "Double check", a second person reviewing the work
再発防止策 saihatsu bōshi saku Recurrence prevention measures
日本損害保険協会 Nihon Songai Hoken Kyōkai The General Insurance Association of Japan

We will update this article if TOPPAN or Sompo Japan publishes more.