Japanese Internet Giant GMO Investigates Data Leak After Customer Information Posted by Hackers

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GMO Internet is probing an alleged data breach of its Onamae cloud desktop service, with hackers reportedly posting stolen customer data. The breach may affect 27,000 servers and follows a ransom demand of about $50 million.

On October 21, 2026, Japanese internet and IT services company GMO Internet discovered unauthorized access to its Onamae Desktop Cloud service, which provides virtualized desktops primarily for financial traders. This security incident led GMO to shut down the service immediately and initiate a thorough investigation. Onamae customers have since been advised to reset their passwords amid reports of unauthorized operations on trading accounts.

GMO Internet stated that a suspected attacker posted information possibly linked to its business and customers, though verification of the data's authenticity and the full impact of the breach remain ongoing. The company estimates that as many as 27,000 servers could be affected.

The incident began with a ransom demand for approximately 8 billion yen (around $50 million). GMO reported the attack to Japanese authorities on October 22 and has committed to providing compensation to affected customers while offering alternative services. Since October 25, the company has been collecting customer devices to scan for malware and assess damage.

Adding context, around the same time, GMO's cybersecurity unit identified a Chinese-made AI-enabled penetration testing tool called Artex being used in cyberattacks targeting companies across Japan. Although no confirmed link between Artex and the Onamae breach exists, Artex has been implicated in attacks on financial institutions in South Korea and Japan. Its developer recently ceased public updates and made the tool closed-source following media reports.

Japan’s Financial Services Agency (FSA) has urged financial firms to bolster cybersecurity defenses, emphasizing basic protections such as vulnerability management, layered defenses, and preparedness for incidents, alongside encouraging the adoption of AI-powered security tools.

The GMO Onamae breach underscores rising cybersecurity challenges in Japan’s financial technology sector, highlighting the growing threat posed by sophisticated hacking tools and the importance of vigilant security practices.