Nikkei Hit by Cyberattack, Personal Data of Over 17,000 Employees Compromised

Japanese media house Nikkei reported a recent data security incident in which hackers accessed employee Slack accounts, compromising the sensitive personal information of over 17,000 staff members.

Japanese media giant Nikkei is among the world’s largest media organisations. Best known for its flagship daily newspaper, The Nikkei, the company has a daily circulation of over 1.7 million and more than 3 million digital subscribers.

In a data security incident notice, Nikkei said that in September it identified an unauthorised external login occurred on Slack, the business chat platform used by Nikkei. The media house immediately launched an investigation, with assistance from external cyber security experts, to determine the nature and scope of the incident.

“An employee’s personal computer was infected with a virus, leading to the leakage of Slack authentication credentials. It is believed that this information was used to gain unauthorised access to employee accounts. The incident was identified in September, and countermeasures such as changing passwords were implemented,” Nikkei said.

The company confirmed that the breach exposed sensitive information—such as names, email addresses, and chat histories—of 17,368 Slack users.

“Personal information used for reporting and writing purposes is not subject to the Personal Information Protection Law which requires reporting in the event of a leak. Considering the incident’s significance and to ensure transparency, we voluntarily reported it to the Personal Information Protection Commission. No leakage of information related to sources or reporting activities has been confirmed,” the media house added.

At the time of publishing, no known hacker group claimed responsibility for the cyber attack on Nikkei. The media house also did not share details on who was behind the attack or whether it had received a ransom demand.