Japanese media giant Nikkei suffered a data breach after attackers infiltrated its internal Slack workspace via malware on an employee’s device, compromising Slack credentials. The intrusion exposed personal details—including names, email addresses, and chat histories—of **17,368 employees and business partners**. While Nikkei confirmed no leakage of journalistic sources or reporting activities, the exposure of internal communications poses a significant reputational risk for a media organization reliant on confidentiality. The company reported the incident to Japan’s Personal Information Protection Commission, though local laws may not have required disclosure. No evidence yet suggests the stolen data has surfaced online, but the breach highlights vulnerabilities in collaboration platforms like Slack, which have become prime targets for credential theft, phishing, and malware-driven attacks. Nikkei reset passwords and pledged to strengthen data protection measures, but the incident underscores the fragility of trust when sensitive corporate communications are exposed.
Source: https://www.theregister.com/2025/11/06/nikkeis_private_chats_go_public/
TPRM report: https://www.rankiteo.com/company/nikkei
"id": "nik0732907110625",
"linkid": "nikkei",
"type": "Breach",
"date": "5/2025",
"severity": "60",
"impact": "3",
"explanation": "Attack with significant impact with internal employee data leaks"{'affected_entities': [{'customers_affected': '17,368 (employees and business '
'partners)',
'industry': ['publishing',
'news media',
'financial information services'],
'location': 'Japan',
'name': 'Nikkei Inc.',
'size': 'large enterprise',
'type': 'media company'}],
'attack_vector': ['malware',
'credential theft',
'compromised employee device'],
'data_breach': {'data_exfiltration': ['confirmed (data accessed)',
'no evidence of public leakage yet'],
'file_types_exposed': ['Slack messages',
'potentially shared documents/files'],
'number_of_records_exposed': '17,368',
'personally_identifiable_information': ['names',
'email addresses'],
'sensitivity_of_data': ['moderate to high (internal chat '
'histories for a media company)'],
'type_of_data_compromised': ['personal identifiable '
'information (PII)',
'corporate communications']},
'description': 'Japanese media company Nikkei suffered a data breach after '
'attackers infiltrated its internal Slack workspace via '
"malware on an employee's device. The breach exposed personal "
'details of 17,368 employees and business partners, including '
'names, email addresses, and Slack chat histories. Nikkei '
"reported the incident to Japan's Personal Information "
'Protection Commission, though not legally required. No '
'evidence of leaked source or reporting data was found, but '
'internal communications were compromised. The company reset '
'passwords and pledged to strengthen data protection measures.',
'impact': {'brand_reputation_impact': ['high (media company built on '
'confidentiality)',
'erosion of trust among '
'sources/partners'],
'data_compromised': ['names',
'email addresses',
'Slack chat histories (including potentially '
'sensitive internal communications)'],
'identity_theft_risk': ['moderate (names + email addresses '
'exposed)'],
'legal_liabilities': ["voluntary reporting to Japan's Personal "
'Information Protection Commission (no '
'confirmed legal obligation)'],
'operational_impact': ['disruption to internal communications',
'potential loss of confidential '
'discussions'],
'systems_affected': ['Slack workspace',
'employee device (initial infection point)']},
'initial_access_broker': {'data_sold_on_dark_web': ['no evidence yet'],
'entry_point': ['malware-infected employee device'],
'high_value_targets': ['Slack workspace',
'internal communications']},
'investigation_status': 'ongoing (no evidence of data appearing online yet)',
'lessons_learned': ['Collaboration platforms (Slack, Teams, etc.) are '
'high-value targets requiring robust security controls',
'Endpoint security is critical to prevent initial malware '
'infections',
'Media organizations must prioritize protecting internal '
'communications to maintain source confidentiality',
'Voluntary disclosure can demonstrate transparency even '
'when not legally required'],
'motivation': ['data exfiltration',
'potential espionage',
'financial gain (hypothetical)'],
'post_incident_analysis': {'corrective_actions': ['Password reset for all '
'affected accounts',
'Enhanced personal '
'information management '
'protocols',
'Planned strengthening of '
'collaboration platform '
'security'],
'root_causes': ['Inadequate endpoint protection '
'leading to malware infection',
'Potential lack of MFA on Slack '
'accounts',
'Insufficient monitoring of '
'collaboration platform access',
'Possible over-reliance on '
'perimeter security without '
'internal controls']},
'recommendations': ['Implement multi-factor authentication (MFA) for all '
'collaboration platforms',
'Enhance endpoint detection and response (EDR) '
'capabilities',
'Conduct regular security audits of third-party SaaS '
'applications',
'Provide employee training on securing workplace chat '
'systems',
'Monitor dark web for potential data leaks',
'Consider network segmentation for sensitive '
'communication channels'],
'references': [{'source': 'The Register',
'url': 'https://www.theregister.com/2023/XX/XX/nikkei_slack_breach/'},
{'source': 'Nikkei Official Statement'},
{'source': 'Proofpoint Research on Collaboration Platform '
'Attacks'}],
'regulatory_compliance': {'regulatory_notifications': ["Japan's Personal "
'Information '
'Protection Commission '
'(voluntary)']},
'response': {'communication_strategy': ['public disclosure',
'internal notifications'],
'containment_measures': ['password resets for affected accounts'],
'enhanced_monitoring': ['planned (for collaboration platforms)'],
'incident_response_plan_activated': True,
'law_enforcement_notified': ["Japan's Personal Information "
'Protection Commission (voluntary)'],
'remediation_measures': ['strengthening personal information '
'management protocols']},
'stakeholder_advisories': ['Internal communications to employees and business '
'partners'],
'title': 'Nikkei Slack Data Breach Exposes 17,000+ Employee and Business '
'Partner Details',
'type': ['data breach', 'unauthorized access', 'malware infection'],
'vulnerability_exploited': ['weak endpoint security',
'lack of multi-factor authentication (MFA) on '
'Slack',
'insufficient monitoring of collaboration '
'platforms']}