Japanese Telco NTT Reports Cyberattack Exposing 12 Million Emails
Japanese telecommunications giant NTT has disclosed a cyberattack impacting an email system used by five internet service providers, potentially exposing 12 million customer email addresses.
Japanese telecommunications company NTT has announced a significant cyberattack that has compromised an email system used to manage customer accounts, webmail services, and email storage for five of its subsidiary internet service providers (ISPs).
The breach, disclosed on July 7, 2026, has potentially exposed the email addresses of up to 12 million customers. The full extent of the compromise and the specific data accessed are still under active investigation by the company and its security teams.
NTT has stated that the affected system is integral to the operations of several ISPs under its umbrella, underscoring the widespread potential impact of this incident. The company is working to determine precisely which customer accounts were affected and what specific information may have been exfiltrated.
While the primary data exposed appears to be email addresses, NTT has not ruled out the possibility that other sensitive information could have been accessed. Customers of the affected ISPs are being advised to remain vigilant against potential phishing attempts or other social engineering tactics that could leverage their exposed email addresses.
In response to the incident, NTT has initiated a thorough investigation into the attack vector and the vulnerabilities exploited. The company is also implementing enhanced security measures to prevent similar breaches in the future and to bolster the overall security posture of its customer-facing systems.
This incident adds to a growing list of data breaches affecting major telecommunications and internet service providers globally, highlighting the persistent threat landscape faced by critical infrastructure operators. The scale of the breach at NTT underscores the importance of robust security protocols and continuous monitoring in safeguarding sensitive customer data.
NTT has committed to providing further updates as the investigation progresses and has established a dedicated support channel for affected customers seeking more information or assistance. The company is also cooperating with relevant regulatory authorities as part of its incident response process.