KOIKE SANSO KOGYO announced a cyberattack, and electronic files suspected of having been leaked were confirmed to have been made public on the internet. Exitium claims to have stolen approximately 5.8 TB of data and suggested that it would sell the data by 13 October.
In an announcement dated 15 October 2026, KOIKE SANSO KOGYO explained that it had restricted connections to its internal network to prevent further damage. Although its investigation to identify the cause and scope of the impact had been completed, some system outages remained and operations were being affected. The company also reconfirmed that electronic files suspected of having been leaked had been made public online. The specific scope and full contents of the information made public remain under investigation.
Exitium claimed to hold approximately 5.8 TB of data, including business documents, information system management screens and materials that may contain personal information. However, the company did not publish evidence substantiating the 5.8 TB figure, and the location and authenticity of the entire dataset have not been confirmed. The attackers had suggested selling the data by 13 October.
Personal information was reportedly stored on the affected servers, and the company says it has reported the matter to the Personal Information Protection Commission as a case involving the risk of an information leak. The authenticity of the materials posted and the source of the leak have not been confirmed.
In a corrected announcement dated 15 October 2026, KOIKE SANSO KOGYO changed the assessment of the impact on consolidated results from “minor” to “currently under review,” with respect to the impact on the earnings announcement schedule for the second quarter of the fiscal year ending March 2027.