Was Nishiyama Seisakusho hit by ransomware?

Nishiyama Seisakusho was listed by the thegentlemen ransomware operation (Japan), and stolen data was published on the group's leak site. Darkfield tracks this disclosure with the original leak post, screenshot and group context.

Who is the thegentlemen ransomware group?

thegentlemen is a ransomware operator tracked by Darkfield. See the full operator dossier for its known victims, sectors targeted, IOCs and leak-site infrastructure.

What data was leaked in the Nishiyama Seisakusho breach?

thegentlemen published data attributed to Nishiyama Seisakusho. Darkfield captured the leak post and a screenshot of the listing.

Ransomware victim disclosure

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Nishiyama Seisakusho Co., Ltd.

listed as Nishiyama Seisakusho · Claimed by Thegentlemen · listed 4 months ago

Age

since listed · data leaked

Status timeline

ListedFeb 6, 2026
Data leakeddate unknown

At a glance

Group: Thegentlemen
Status: Data leaked
Country: Japan
Listed on leak site: Feb 6, 2026

About the victim

AI dossier — public-source company profile

Nishiyama Seisakusho Co., Ltd. (株式会社西山製作所) is a Japanese manufacturer specializing in small-diameter precision steel tubes, founded in 1949. The company is particularly known for drawn steel tubes with outer diameters of 10mm or less, holding a high market share in tubes of 6mm and under. It operates facilities including a head office/factory, an Akita factory, and a Philippine subsidiary, and also produces heat transfer tubes and heat exchangers.

Industry: Precision Steel Tube Manufacturing
Founded: 1949

Attack summary

Severity: medium — Data is marked as published, indicating confirmed exfiltration and public disclosure, but the specific nature, volume, and sensitivity of the data cannot be determined from the available post content, and no regulated/critical sector data is confirmed.

The group 'thegentlemen' claims to have attacked Nishiyama Seisakusho and has published data (disclosed status: data_published), though the leak post content was inaccessible due to a bot-verification page, leaving specific claims about encryption or exfiltration unverifiable from the post itself.

medium

What the group claims

nishiyama-ss.co.jp zoominfo.com/c/nishiyama-seisakusho-co-ltd/482975122 Nishiyama Seisakusho Co., Ltd. specializes in the production of precision machinery and components, particularly focusing on high-quality manufacturing since its establishment in 1949. The company offers a range of products including precision gears and mechanical parts, catering to various industries. Their intended clients include businesses in need of reliable and precise mechanical solutions. With a commitment to quality

The leak post

captured from the group's site

Gentlecloud Protection 🛡️ Gentlecloud Verifying your browser... Initializing security checks... I'm not a bot

Sources

Victim sitenishiyama-ss.co.jp
Leak posthttp://tezwsse5czllksjb7cwp65rvnk4oobmzti2znn42i43bjdfd2prqqkad.onion

Source

Indexed 4 months 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.

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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 483 public disclosures across our corpus. First observed on a leak site on September 9, 2025; most recent post June 11, 2026. The operation is currently active.

Also tracked as: the gentlemen.

Timeline of this disclosure

February 6, 2026Nishiyama Seisakusho listed by thegentlemenon the group's public leak site

Other recent disclosures by thegentlemen

thegentlemen has been linked to 483 public victims on Darkfield. A sample of the most recent:

See the full thegentlemen dossier →

Sector and geography

Geographically, Nishiyama Seisakusho is reported in Japan, a country with 108 ransomware disclosures in our corpus.

If your organisation is affected

A listing by thegentlemen means Nishiyama Seisakusho appeared on a ransomware extortion site and data attributed to it has been published. If this is your organisation, or a supplier you depend on, the priority is to confirm the intrusion and contain it before the window to act closes.

Engage your incident-response team and preserve forensic evidence before remediating — do not wipe affected systems first.
Force a password reset and revoke active sessions for exposed accounts; rotate any credentials, API keys or certificates that may have been in the stolen data.
Assess regulatory notification duties (GDPR, NIS2, sector regulators) — many carry a 72-hour reporting clock from awareness.
Monitor for the data appearing on thegentlemen's leak site and across paste and breach channels, and brief downstream partners who may be exposed through you.

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.