Disclosure context

About thegentlemen

thegentlemen is a ransomware group that emerged in September 2025, operating with apparent financial motivations based on their broad targeting of commercial sectors. The group has documented 267 victims across multiple countries, with primary focus on the United States, Thailand, France, Brazil, and India. Their targeting strategy demonstrates a preference for high-value sectors including manufacturing, technology, healthcare, and financial services organizations. Given the group's recent emergence and limited public documentation from established threat intelligence sources such as CISA, FBI, or major security research firms, specific details regarding their country of origin, operational structure, attack methodologies, encryption techniques, and whether they employ ransomware-as-a-service models remain unclear. The relatively high victim count of 267 in a short operational timeframe since September 2025 suggests either an aggressive campaign pace or potential inflation of victim numbers through affiliate operations, though without corroborating intelligence reports, the group's exact operational capabilities and notable campaigns cannot be definitively established. Current intelligence indicates the group remains active as of late 2025, though comprehensive threat profiling requires additional validated reporting from authoritative cybersecurity sources. The group has been linked to 424 public disclosures across our corpus. First observed on a leak site on September 9, 2025; most recent post May 18, 2026. The operation is currently active.

Also tracked as: the gentlemen.

Timeline of this disclosure

May 6, 2026Nostrum listed by thegentlemenon the group's public leak site

Sector and geography

This disclosure adds to ransomware activity in the Not Found sector, which has 4,859 disclosures indexed across all operators we track. Geographically, Nostrum is reported in JP, a country with 88 ransomware disclosures in our corpus.

How we know this. Darkfield monitors public ransomware leak sites continuously, archiving every new disclosure and the data later released against the victim. Each entry on this page is sourced from the operator's own publication and cross-checked against complementary OSINT feeds (RansomLook, ransomware.live, RansomWatch). We do not collect or host stolen data — only the metadata, timestamps and screenshots needed to make the public disclosure searchable and accountable. Records here are corrected when the original post is edited, retracted, or merged with another disclosure.

Ransomware victim disclosure

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Nostrum

Claimed by thegentlemen · listed 15 days ago

14d

Age

since listed · data leaked

Status timeline

Listed
May 6, 2026
Data leaked

At a glance

Group: thegentlemen
Status: Data leaked
Country: JP
Sector: Not Found
Listed on leak site: May 6, 2026

About the victim

AI dossier — public-source company profile

Nostrum Corporation (株式会社ノストラム) is a Tokyo-based Japanese technology company founded in 1991. The company specialises in smartphone application development (iOS and Android), web system development and website construction, hardware board design/manufacturing, and e-learning software. Its flagship self-developed product is SMART SPI, an online job-aptitude-test preparation platform used by university students and job seekers across Japan.

Industry: IT Services & Software Development (Smartphone Apps, Web Systems, Hardware Solutions)
Address: Japan (Tokyo inferred from phone prefix 03-3512-0871); full street address not stated on public site
Founded: 1991

Attack summary

Severity: high — Data has been published (data_published status) and the victim's own site confirms a ransomware infection causing service disruption. The e-learning platform likely holds PII of student and job-seeker users; prior development work includes medical, pharmaceutical, and financial sector systems suggesting sensitive client data may be present. Confirmed exfiltration and operational disruption together warrant a high rating.

The group 'thegentlemen' claims a ransomware attack that infected Nostrum's servers; the company's own website (dated 2026-05-08) confirms a ransomware infection causing suspension of its learning-support service. The disclosure status is 'data_published', indicating the attackers claim to have exfiltrated and published data, though no specific data size or ransom amount was stated.

high

Data the group says was taken

AI dossier — extracted from the leak post

Company internal systems data
Customer/user data from e-learning platform (SMART SPI)
Web and mobile application project files
Business operational data

What the group claims

nostrum.co.jp Nostrum Corporation, based in Japan, was founded in 1991 and specializes in smartphone app development, web system development, and website construction. The company is represented by Ryoichi Jono and is registered on the J-GoodTech platform as a verified Japanese technology business. One of their flagship self-developed products is a job aptitude test preparation tool — a simulation platform replicating real SPI, TG-WEB, and similar employment exam interfaces used by major Japanese companies

Sources

Victim sitenostrum.co.jp

Source

Indexed 15 days ago

This page surfaces a public ransomware disclosure indexed by Darkfield. Original posts come from the operator's own leak site; we cross-check against ransomware.live, RansomLook and RansomWatch where applicable. Share this URL freely.