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Home » Nikkei Reports 17,000 Affected by Slack Account Hack Data Breach
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Nikkei Reports 17,000 Affected by Slack Account Hack Data Breach

Staff WriterBy Staff WriterNovember 6, 2025No Comments3 Mins Read0 Views
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Fast Facts

  1. Hackers stole over 17,000 Nikkei employee Slack accounts using malware that harvested credentials from personal computers.
  2. The breach exposed names, email addresses, and chat histories, but no reporting or source information was confirmed as leaked.
  3. Nikkei discovered the hack in September, changed passwords, and voluntarily reported it to Japan’s Personal Information Protection Commission.
  4. Infostealer malware has compromised over 270,000 Slack credentials nationwide, with Nikkei experiencing previous cyberattacks, including a 2022 ransomware incident.

Underlying Problem

Recently, Japanese media giant Nikkei revealed that hackers infiltrated its internal systems by compromising employee Slack accounts. The breach was traced back to malware that stole login credentials from an employee’s personal computer, which attackers then used to access over 17,000 Slack profiles—covering both staff and business partners—and harvest personal data like names, email addresses, and chat histories. Although no sensitive source or reporting information was confirmed to be leaked, the company swiftly changed passwords and reported the incident voluntarily to Japan’s Personal Information Protection Commission, emphasizing their commitment to transparency despite not being legally obligated to do so. The attack highlights the persistent threat posed by infostealer malware, which has compromised hundreds of thousands of Slack accounts globally, and signals a recurring challenge for Nikkei, which previously experienced a ransomware attack in 2022 impacting customer data.

The incident underscores ongoing vulnerabilities in corporate cybersecurity, particularly involving the theft of credentials via malware, and raises concerns about the safeguarding of confidential information. It also illustrates how cybercriminals exploit credential theft to gain unauthorized access to digital platforms, potentially jeopardizing sensitive communications and business relationships. As a reputable provider of financial and news media, Nikkei’s disclosure not only informs the public about a serious breach but also reflects the precarious landscape of digital security, where breaches can occur unexpectedly and have widespread implications for both organizations and their stakeholders.

What’s at Stake?

The incident reported by Nikkei, where 17,000 entities were impacted due to a data breach stemming from a Slack account hack, underscores a critical vulnerability that any business could face; if an attacker gains access to your company’s communication platform, they can easily compromise sensitive information, disrupt operations, and erode customer trust, ultimately leading to sizable financial losses, reputational damage, and legal repercussions.

Fix & Mitigation

In today’s fast-evolving digital landscape, swift action following a data breach is crucial to minimize damage, protect sensitive information, and restore trust. When, as in this case, a significant number of Nikkei users are impacted by a breach originating from a Slack account hack, immediate and effective mitigation becomes paramount.

Containment Measures

  • Isolate compromised accounts to prevent further unauthorized access.
  • Disable or suspend the affected Slack accounts temporarily.

Analysis and Assessment

  • Conduct thorough investigations to understand the breach scope and methods used.
  • Identify affected systems, data, and users quickly.

Communication

  • Notify affected users promptly, providing guidance on further steps and precautions.
  • Coordinate with internal stakeholders and external partners to ensure clear messaging.

Recovery Actions

  • Reset passwords and implement multi-factor authentication on all related accounts.
  • Patch security vulnerabilities exploited during the breach.

Long-term Improvements

  • Review and strengthen security policies and access controls.
  • Conduct staff training on security best practices to prevent future incidents.
  • Regularly update and test incident response plans to optimize response times.

Continue Your Cyber Journey

Explore career growth and education via Careers & Learning, or dive into Compliance essentials.

Learn more about global cybersecurity standards through the NIST Cybersecurity Framework.

Disclaimer: The information provided may not always be accurate or up to date. Please do your own research, as the cybersecurity landscape evolves rapidly. Intended for secondary references purposes only.

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John Marcelli is a staff writer for the CISO Brief, with a passion for exploring and writing about the ever-evolving world of technology. From emerging trends to in-depth reviews of the latest gadgets, John stays at the forefront of innovation, delivering engaging content that informs and inspires readers. When he's not writing, he enjoys experimenting with new tech tools and diving into the digital landscape.

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