Japanese publishing giant Nikkei said its Slack messaging platform was compromised, exposing personal information for more than 17,000 employees and business partners. The company, which owns the Financial Times and The Nikkei newspaper, has about 3.7 million digital paid subscriptions, more than 40 affiliated companies and over 1,500 journalists across 37 foreign editorial bureaus.
Nikkei said attackers gained access to employee Slack accounts by using authentication credentials that were stolen after an employee’s computer was infected with malware. The company discovered the incident in September and took immediate security measures, including mandatory password changes.
The company said the potentially leaked information includes the names, email addresses and chat histories for 17,368 individuals registered on Slack. Nikkei described the incident as significant but provided no public evidence in its statement that would indicate whether the stolen data has been published or otherwise disseminated.
Nikkei said the information does not fall under Japan’s Personal Information Protection Law, which requires reporting for certain types of breaches, but the publisher voluntarily notified the Personal Information Protection Commission and emphasized transparency. The company also said no information related to confidential sources or reporting activities has been confirmed as compromised.
The announcement follows earlier security incidents involving the publisher: a May 2022 ransomware attack on a Nikkei subsidiary in Singapore that affected a server said to likely contain customer data, and a 2019 business email compromise in which Nikkei lost roughly $29 million after an employee was tricked by scammers.
Nikkei did not name the attackers or say whether the stolen credentials were used elsewhere, and it said it will further strengthen personal information management to prevent recurrence.