Japanese publishing company Nikkei suffers Slack compromise exposing data of over 17,000 people
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Nikkei Inc., one of the world's largest media corporations and owner of The Financial Times, is reporting a data breach affecting its Slack communications platform.
The incident (link in Japanese) was discovered in September 2025 and compromised the personal information of 17,368 employees and business partners through unauthorized access to the company's messaging system.
The incident is caused by a personal computer of an employee's that became infected with malware, which subsequently harvested the employee's Slack authentication credentials. Attackers used the stolen credentials to gain unauthorized access to the company's Slack workspace, potentially exposing sensitive internal communications and personal information.
After detecting the incident Nikkei forced mandatory password changes for all affected accounts. The exposed data includes:
- Full names of registered Slack users
- Email addresses
- Complete chat histories and internal communications
Nikkei claims that the compromised information does not fall under the mandatory reporting requirements of Japan's Personal Information Protection Law, but Nikkei voluntarily notified Japan's Personal Information Protection Commission about the breach.
Nikkei has informed affected individuals and provided contact information for inquiries related to the breach.
