Nikkei Inc., a leading Japanese business news publisher, experienced a security breach after an employee’s personal computer was infected with malware, leading to unauthorized access to its internal Slack workspace. The incident resulted in the exfiltration of authentication credentials, exposing sensitive internal communications and personal data of up to **17,368 individuals**, including full names, email addresses, and chat histories. While no evidence suggests journalistic sources or editorial materials were compromised, the breach highlights vulnerabilities tied to personal device usage for corporate access. Nikkei responded with containment measures (password resets, access reviews) and voluntarily reported the incident to Japan’s Personal Information Protection Commission, emphasizing transparency and a commitment to strengthening data protection. No public leaks or direct misuse of the data have been confirmed to date.
Source: https://cyberinsider.com/nikkei-suffers-slack-breach-after-employee-pc-malware-infection/
TPRM report: https://www.rankiteo.com/company/nikkei
"id": "nik31101431110425",
"linkid": "nikkei",
"type": "Breach",
"date": "11/2025",
"severity": "60",
"impact": "3",
"explanation": "Attack with significant impact with internal employee data leaks"{'affected_entities': [{'customers_affected': '17,368 individuals',
'industry': ['Publishing',
'News',
'Financial Reporting'],
'location': 'Japan (with international operations)',
'name': 'Nikkei Inc.',
'size': 'Large (Owns Financial Times, Nihon Keizai '
'Shimbun)',
'type': 'Media Organization'}],
'attack_vector': ['Malware Infection on Personal Device',
'Credential Stuffing/Reuse'],
'data_breach': {'data_exfiltration': True,
'file_types_exposed': ['Slack Messages/Logs', 'User Profiles'],
'number_of_records_exposed': '17,368',
'personally_identifiable_information': ['Full Names',
'Email Addresses'],
'sensitivity_of_data': ['Moderate (PII and Internal Chats, '
'but No Journalistic Sources or '
'Editorial Materials)'],
'type_of_data_compromised': ['Personal Identifiable '
'Information (PII)',
'Internal Communications']},
'date_detected': '2023-09',
'description': 'Nikkei Inc., one of Japan’s largest business news publishers, '
'disclosed that its internal Slack workspace suffered '
'unauthorized access due to the malware infection of an '
'employee’s personal computer. The breach resulted in the '
'exfiltration of authentication credentials, raising concerns '
'over the potential leakage of sensitive internal '
'communication and personal information. Up to 17,368 '
'individuals may be affected, with leaked information '
'potentially including full names, email addresses, and chat '
'histories. No evidence suggests journalistic sources or '
'editorial materials were accessed.',
'impact': {'brand_reputation_impact': ['Potential Erosion of Trust Among '
'Employees and Stakeholders'],
'data_compromised': ['Full Names',
'Email Addresses',
'Slack Chat Histories (Internal '
'Communications)'],
'identity_theft_risk': ['Moderate (Due to Exposed PII)'],
'operational_impact': ['Potential Disruption to Internal '
'Communication',
'Investigation and Remediation Efforts'],
'systems_affected': ['Slack Workspace']},
'initial_access_broker': {'entry_point': 'Malware-infected personal computer '
'of an employee',
'high_value_targets': ['Slack Workspace '
'Credentials']},
'investigation_status': 'Ongoing (No public leaks observed as of disclosure)',
'lessons_learned': ['Risks of using personal devices for corporate access, '
'especially for communication platforms like Slack.',
'Importance of enforcing MFA and strong credential '
'policies for all corporate systems, including '
'third-party tools.',
'Need for continuous monitoring of anomalous logins and '
'access patterns.'],
'post_incident_analysis': {'corrective_actions': ['Password resets and access '
'reviews for Slack '
'accounts.',
'Enhanced monitoring for '
'anomalous logins.',
'Commitment to reinforcing '
'data protection measures '
'to prevent recurrence.'],
'root_causes': ['Malware infection on an '
'employee’s personal computer '
'leading to credential theft.',
'Lack of MFA or sufficient access '
'controls for Slack.',
'Use of personal devices for '
'corporate communication without '
'adequate security measures.']},
'recommendations': ['Implement Mandatory Multi-Factor Authentication (MFA) '
'for all corporate accounts, including Slack.',
'Enforce stricter policies on the use of personal devices '
'for accessing corporate systems.',
'Conduct regular security awareness training to educate '
'employees on phishing and malware risks.',
'Deploy endpoint detection and response (EDR) solutions '
'to monitor and block malware infections on personal '
'devices used for work.',
'Segment corporate networks to limit lateral movement in '
'case of credential compromise.'],
'references': [{'source': 'Nikkei Inc. Official Statement (via media '
'reports)'}],
'regulatory_compliance': {'regulatory_notifications': ['Voluntary '
'Notification to '
'Japan’s Personal '
'Information '
'Protection Commission '
'(PIPC)']},
'response': {'communication_strategy': ['Voluntary Notification to Personal '
'Information Protection Commission',
'Public Disclosure for Transparency'],
'containment_measures': ['Password Resets for Affected Accounts',
'Access Reviews',
'Revoking Compromised Credentials'],
'enhanced_monitoring': ['Monitoring for Unauthorized Access or '
'Data Leaks'],
'incident_response_plan_activated': True,
'remediation_measures': ['Reinforcing Data Protection Measures',
'Reviewing Access Controls for Slack']},
'stakeholder_advisories': ['Internal communication to employees about the '
'breach and remediation steps.'],
'title': "Unauthorized Access to Nikkei Inc.'s Internal Slack Workspace via "
'Malware-Infected Personal Computer',
'type': ['Data Breach', 'Unauthorized Access', 'Credential Theft'],
'vulnerability_exploited': ['Weak/Leaked Credentials',
'Lack of Multi-Factor Authentication (MFA) on '
'Slack',
'Use of Personal Device for Corporate Access']}