Nostrum Listed by thegentlemen Ransomware Group: Ransomware Claim — What’s Alleged & What To Do
Nostrum was listed by thegentlemen ransomware group on May 06, 2026, with internal files reported exfiltrated in the attack. An undisclosed number of people may be affected; check whether your data was involved and take protective steps.
Breaking down the breach
The incident came to light through a listing on thegentlemen’s leak site on May 06, 2026. The only detail provided is that internal files were taken. No information has been released about the timing of the intrusion, the volume of data, the encryption status of systems, or whether a ransom demand was issued or met.
Public records do not indicate any official statement from Nostrum confirming or denying the claims. The scale of exposure and the method of initial access remain undisclosed.
Who is thegentlemen?
Thegentlemen is a ransomware operator that maintains a leak site where it lists organizations it claims to have targeted. Groups of this type typically encrypt systems and threaten to publish stolen data if demands are not met. Their listings serve as public assertions rather than independently verified incidents.
No additional claims specific to Nostrum beyond the listing itself have been documented in available reports.
About Nostrum
Nostrum Corporation, operating from nostrum.co.jp, was established in 1991 in Japan. It focuses on smartphone application development, web system development, and website construction. The company is represented by Ryoichi Jono and appears on the J-GoodTech platform as a verified technology business.
One of its self-developed products is a simulation platform that replicates employment examination interfaces such as SPI and TG-WEB used by major Japanese companies. Organizations in this sector routinely handle client project files, internal development records, and user-related test data.
What data was at risk
The listing refers only to “internal files.” No inventory of specific file types, databases, or personal information has been published. The exact contents therefore remain unconfirmed.
- Internal files exfiltrated in ransomware attack
What's at stake
Organizations that develop employment-preparation tools can hold records that include test content, client configurations, and administrative correspondence. Exposure of such material could affect the confidentiality of proprietary exam simulations and any associated business communications.
For individuals whose information appears in those files, risks are limited to whatever data elements were present; without a confirmed list, the practical impact cannot be quantified.
Were you affected?
Check any accounts associated with Nostrum or its services for unusual activity. Monitor official statements from the company for further details. Readers can run a free exposure scan of their email address against known breach data sets to see whether their information appears in publicly referenced incidents.
AICompiled with AI assistance from public sources and published under our editorial standards.
How this breach connects
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Publicly posted by thegentlemen — unverified claim, pending independent verification
Breach listings — particularly those originating from ransomware or leak sites — are third-party claims that may be unverified, incomplete, or inaccurate. A listing does not by itself confirm that a breach occurred or that any specific data was exposed. Severity is an automated assessment, not a definitive rating. Verification status is shown where available.
Attributions to threat groups and methods reflect public reporting and, in some cases, unverified claims made by the groups themselves; they may be incomplete or later revised. Recent Breaches and GalaxyWarden are independent and are not affiliated with, and do not endorse, any company or group named on this page. This information is aggregated from public sources for awareness only and is not legal, security, or investment advice.