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[Resolved][Severity: Moderate][Misdelivery]

Mitsubishi Gas Chemical: HR system contractor T4C emailed a file with names and staff numbers of 2,092 former employees to another company

A worker at HR system contractor T4C mailed a file with names and staff numbers of 2,093 Mitsubishi Gas Chemical former and current staff to another firm.

Disclosed

2026-10-16

Organizations involved

2

Leaked or at risk

2.1K

2,093

Downtime

Unknown

What happened

  1. A T4C worker attached a file for the contract work to an email meant for another company. The recipient got in touch the same day, and the file was confirmed deleted without being opened. [1]

  2. T4C and Mitsubishi Gas Chemical reported to the Personal Information Protection Commission. [1]

  3. Mitsubishi Gas Chemical disclosed it. [1]

Impact

Names and staff numbers of all 2,092 people who left between 31 October 2005 and 31 July 2025, and of one current employee. No secondary harm has been found. Because former employees are hard to reach one by one, the public notice stands in for direct contact. [1]

Response

T4C was asked to stop sending files by email as a rule and to check every email before sending. Oversight of contractors will also be tightened. [1]

Timeline

  1. Started, Detected 2026-09-16
  2. Disclosed 2026-10-16
  3. 30 days

Attack or cause

Method
[Misdelivery]
Impact
[Data leak]
Entry point
E-mail

Data exposed or at risk

[Name][Employment]

Supply chain

T4C Inc.

[Breached]

Organizations listed on this site
2

Organizations involved

Open in organization search

Sources

  1. [1][Official]当社業務委託先における個人情報を含むメールの誤送信について（お詫び）Mitsubishi Gas Chemical · 2026-10-16