A massive data breach has exposed up to 14.2 million email logins at six Japanese internet service providers (ISPs), leaving customers vulnerable to account hijacks and other forms of cyber attacks. The incident, which was disclosed by KDDI Corporation on June 17, involves a vulnerability in an unnamed third-party software used by the company’s email system.
The compromised email system is used by five other ISPs in Japan: STNet, Inc., JCOM Co., Ltd., Chubu Telecommunications C., Inc., NIFTY Corporation, and BIGLOBE Inc. These companies, which collectively serve millions of customers, have now been notified by KDDI about the potential exposure of their email addresses and passwords.
KDDI’s investigation suggests that the hackers exploited a vulnerability in the third-party software to gain access to the company’s email system. While the company has taken immediate action to block the attacker and implement defense measures, there is still a possibility that customers’ email addresses and passwords were obtained by unauthorized parties. This raises serious concerns about the security of online accounts and the potential for cyber attacks.
The scope of the breach is significant, with KDDI warning that up to 14.2 million customers may have been affected. This figure includes current and former customers, as well as inactive accounts that may no longer be in use. While some passwords were stored in hashed and/or encrypted form, which makes them more difficult for attackers to abuse, the exact number of plaintext passwords exposed remains unknown.
KDDI has notified Japan’s Personal Information Protection Commission and the Ministry of Internal Affairs and Communications about the incident and is working with affected ISPs to implement additional security measures. In the meantime, customers are advised to reset their email account passwords as soon as possible and consider enabling two-factor authentication (2FA) for added protection.
This breach serves as a stark reminder of the importance of robust cybersecurity measures in protecting online accounts. With hackers increasingly targeting vulnerable software vulnerabilities, it’s essential for companies to prioritize security and regularly update their systems to prevent similar incidents from occurring. For individuals, this incident highlights the need to remain vigilant about password management and take proactive steps to protect their online identities.
In light of this breach, customers are advised to take immediate action to secure their email accounts. This includes resetting passwords, enabling two-factor authentication, and regularly monitoring account activity for suspicious behavior. By taking these precautions, individuals can reduce their risk of falling victim to cyber attacks and minimize the potential consequences of a data breach.
Source: Bleeping Computer — 2026-06-28