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Data Breach at Nikkei Inc. Due to a Computer Virus, Employee Info leaked

Cyber Security

Nikkei Data Breach Exposes Employee Information

Business Honor
11 November, 2025

Nikkei reports data breach affecting over 17,000 employees and partners after unauthorized access to Slack accounts

Confidential database of over 17,000 employees and business partners of Nikkei Inc. has been compromised after unauthorized access to the company's business chat platform. Nikkei, one of Japan's largest media companies, disclosed the intrusion, stating it had discovered the hacking in September. "An unauthorized external login occurred on 'Slack', the business chat platform that Nikkei Inc. uses for some of its operations," it said in a statement. This incident raised suspicions that information pertaining to both employees and business partners had been leaked.

According to Nikkei, the hack was made possible by access to a personal computer belonging to an employee that had become infected with a malware, leading to the personal computer's authentication credentials to Slack being leaked. "This information was what permitted unauthorized access to employee accounts on Slack," it said. Nikkei volunteered to report the security incident to the Personal Information Protection Commission.

Potentially leaked information includes the names, email addresses and chat histories for 17,368 individuals registered on Slack according to the company. "Countermeasures such as changing passwords were implemented," it said. "No leakage of information related to sources or reporting activities has been confirmed. We take this incident seriously and will further strengthen personal information management to prevent any recurrence," it added. In Japan, the Act on the Protection of Personal Information requires organizations to report data leaks. However, personal information used for reporting and writing purposes is generally exempt from this obligation.