Japanese media powerhouse Nikkei has confirmed a significant data breach that has potentially compromised the personal information of over 17,000 employees and business associates. This breach occurred when hackers infiltrated the company’s internal Slack messaging platform, raising serious concerns about cybersecurity vulnerabilities within corporate communication tools.
Based in Tokyo, Nikkei, widely recognized for its flagship publication, The Nikkei, reported that unauthorized access was achieved through stolen login credentials from an employee whose personal computer had been infected with malware. The compromised information may include names, email addresses, and chat histories of 17,368 individuals registered on the internal workspace. Although Nikkei utilizes Slack for various operations, it has not specified which departments or subsidiaries were impacted by this incident.
The company stated that the breach was discovered in September 2025 and emphasized its commitment to enhancing personal information management practices to prevent future occurrences. Importantly, Nikkei confirmed that no data related to journalistic sources or reporting was breached and announced a series of security measures, including enforced password resets for affected individuals.
While the compromised data is not directly protected under Japan’s Personal Information Protection Law, Nikkei took the initiative to inform the country’s Personal Information Protection Commission, citing the matter’s significance and a desire for transparency. This incident marks another cyber challenge for the organization; in May 2022, its Singapore subsidiary faced a ransomware attack that potentially jeopardized customer data. Additionally, in September 2019, Nikkei America suffered a business email compromise that resulted in a loss of $29 million.
Cybersecurity experts are highlighting this breach as a critical reminder of the risks associated with hybrid work environments, where employees use personal devices for corporate access. This situation often leads to increased vulnerability due to diminished oversight and control over non-enterprise-managed endpoints. The MITRE ATT&CK framework elucidates this breach, with potential tactics including initial access via phishing or malware deployment, persistence enabled through unauthorized credentials, and potential privilege escalation through the compromised employee account.
Andy Ward, a senior vice president at Absolute Security, noted that the breach emphasizes the critical need for organizations to implement robust access controls and maintain visibility over all devices accessing corporate resources. As the lines between personal and professional technology blur, the necessity for comprehensive security practices has never been more urgent.
Max Heinemeyer, global field chief information security officer at Darktrace, echoed concerns about vulnerabilities in Software as a Service (SaaS) applications. While the convenience of SaaS can streamline IT operations, it can also mask security gaps that are not discovered until a breach occurs. He suggested organizations must prioritize monitoring for atypical activity, such as unusual logins and email behaviors, to identify potential threats early.
Furthermore, the need for checks and balances in security protocols cannot be overstated. Visibility into network activity is paramount; organizations that fail to monitor their environments may leave themselves open to more sophisticated attacks. This breach serves as a stark reminder of the complex landscape businesses must navigate as they balance operational efficiency with cybersecurity resilience.
