Nikkei Dev System Credential Leak Exposes 1.8M Records, 150K With PII, No Cards Compromised

Nikkei Inc., a major Japanese financial news publisher, disclosed a new data breach that exposed personal information belonging to 1.83 million people. The breach occurred when unauthorized users gained entry to a cloud-based system used for software development during the early hours of October 7.

The company stated that attackers used previously stolen credentials to enter the system. Nikkei revoked these compromised login details. The firm notified Japan’s Personal Information Protection Commission on October 11 and is currently examining the scope of the breach. The company is working to determine the cause of the incident and will implement necessary measures to strengthen security.

Data exposure details

Approximately 150,000 of the exposed records contain personally identifiable information. This subset includes full names, email addresses, physical addresses, telephone numbers, and dates of birth. Email addresses were present in about 120,000 of these records. The remaining 1.68 million records contain data that cannot identify specific individuals. Nikkei confirmed that no credit card information was included in the leaked data.

Recent security incidents

This event marks the third cybersecurity incident Nikkei has disclosed in roughly a month. Earlier this month, the company reported a breach from late July where hackers compromised an employee’s Google Workspace account. In September, Nikkei announced that threat actors hijacked a Microsoft 365 account to send spear-phishing emails to staff. These recent events follow a ransomware attack disclosed in May 2022 and a Slack account compromise reported in November 2025.

Affected individuals and next steps

Nikkei stated it will send individual notifications to all affected parties. As of October 16, the company reported no evidence that the accessed information was misused or leaked online. The firm also noted no signs of system compromise, data tampering, or service outages resulting from this specific incident. Nikkei apologized for the breach and said it is working urgently to establish the extent of the damage.

Our take on the response

Nikkei has revoked the abused credentials and notified regulators. The company states it has no evidence of data misuse or system tampering as of October 16. Nikkei is examining the scope of the breach and determining the cause. The firm promises to implement necessary measures to strengthen security. Individual notifications will be sent to those affected.

For customers and users

If you are a Nikkei subscriber or employee, expect an individual notification if your data was involved. Check your email for official messages from Nikkei before clicking any links. Be wary of follow-up scams claiming to help with "data recovery" or "account

Background: Credential leaks

You leave credentials open to theft by reusing passwords, ignoring multi-factor authentication, storing secrets in plain text, and allowing weak session management. Each mistake creates a direct path for attackers to access your accounts. Fix these issues by using a password manager, enforcing hardware keys, and rotating secrets regularly.

Read the full guide: 7 Credential Leak Mistakes That Expose Your Accounts

What to do and how to stay safe

• Least privilege prevents lateral movement by limiting what any single user or process can access.
• Offline backups ensure recovery even if the ransomware encrypts your primary storage and network shares.
• Disabling macros stops the most common initial entry point for ransomware delivered via documents.

Ransomware succeeds when it can execute code and access files freely. Restrict permissions and isolate backups to remove its ability to function.

Step-by-step guide: How to Stop Ransomware: 3 Layers That Actually Work

General security guidance from the DataSafe Radar newsroom. It is not confirmed advice from the organisations named in this story.