Disclosure context

About netrunner

Based on the limited publicly available information, netrunner is a relatively new ransomware group that first emerged in April 2026 with documented attacks against at least six organizations. The group appears to be financially motivated, targeting a diverse range of sectors including healthcare, consumer services, telecommunications, manufacturing, and agriculture across multiple countries including Japan, the United States, Jordan, Italy, and South Korea. Due to the recent emergence of this group and limited public reporting from established threat intelligence sources, detailed information about their country of origin, operational affiliations, specific attack methodologies, encryption techniques, or whether they operate as a Ransomware-as-a-Service model remains undocumented by major cybersecurity organizations such as CISA, FBI, or Mandiant. The group's targeting pattern suggests opportunistic victim selection rather than geopolitically motivated attacks, given the broad geographic and sectoral distribution of their documented victims. No major high-profile campaigns or significant law enforcement actions against netrunner have been publicly reported by reputable security researchers at this time. Given the group's recent emergence in 2026, current activity status and operational capabilities require further monitoring and analysis by the cybersecurity community. The group has been linked to 9 public disclosures across our corpus. First observed on a leak site on April 3, 2026; most recent post May 16, 2026. The operation is currently active.

Timeline of this disclosure

April 3, 2026Nippon Medical School Musashi Kosugi Hospital listed by netrunneron the group's public leak site

Sector and geography

This disclosure adds to ransomware activity in the Healthcare sector, which has 1,779 disclosures indexed across all operators we track. Geographically, Nippon Medical School Musashi Kosugi Hospital 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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Nippon Medical School Musashi Kosugi Hospital

Claimed by netrunner · listed 2 months ago

47d

Age

since listed · data leaked

Status timeline

Listed
Apr 3, 2026
Data leaked

At a glance

Group: netrunner
Status: Data leaked
Country: JP
Sector: Healthcare
Listed on leak site: Apr 3, 2026

About the victim

AI dossier — public-source company profile

Nippon Medical School Musashi Kosugi Hospital is a 372-bed regional teaching hospital located in Nakahara-ku, Kawasaki (Musashi-Kosugi area), affiliated with Nippon Medical School. Established in 1937, it operates 36 clinical departments offering emergency and critical care, ICU, NICU, perinatal and pediatric care, cancer treatment, and minimally invasive procedures. The hospital serves as a regional hub with disaster-resistant facilities, an on-site heliport, and holds accreditation from the Japan Council for Quality Health Care.

Industry: Hospital & Healthcare Services (Teaching Hospital)
Address: 1-383 Kosugicho, Nakahara-ku, Kawasaki-shi, Kanagawa 211-8533, Japan
Employees: 902
Founded: 1937

Attack summary

Severity: critical — Confirmed exfiltration and encryption of data from a hospital, with an estimated 100 million records at stake including patient PII and medical data — constituting regulated sensitive health information at large scale. The hospital itself has publicly acknowledged the breach and personal information leakage.

The NetRunner group claims to have both encrypted and exfiltrated data from the hospital, with approximately 100 million records reportedly involved across 902 files. The hospital's own public website confirms a cyberattack resulting in personal information leakage, with a seventh incident report posted as of April 2026.

critical

Data the group says was taken

AI dossier — extracted from the leak post

Patient personal information
Medical records
Hospital operational data
Staff information
Clinical department records

What the group claims

Nippon Medical School Musashi Kosugi Hospital is a 372-bed regional teaching hospital in Nakahara-ku, Kawasaki (Musashi-Kosugi area), affiliated with Nippon Medical School. Established in 1937, it offers comprehensive services across 36 clinical departments, including emergency and critical care, ICU, NICU, perinatal and pediatric care, cancer treatment, and minimally invasive endovascular procedures. The hospital serves as a regional hub with disaster-resistant facilities and an on-site heliport, and emphasizes advanced, patient-centered care and medical education.

The leak post

captured from the group's site

NetRunner Leak NetRunner Leak Seoyon E-Hwa Summit eoyonehap.com eoyoneh.com India South Korea KRX:200880 120M 1500 Locked, Exfiltrated Seoyon E‑Hwa Summit is a subsidiary of Seoyon E‑Hwa that manufactures automotive components, operating as part of Seoyon E‑Hwa’s international production network. Access Data GEG Telecomunicazioni geg.it Monza, Lombardy, Italy N/A N/A N/A Locked, Exfiltrated GEG srl (est. 1981) designs and builds integrated mobile radio systems across Italy. Over 35 years it served 500+ public administrations and manages 100,000+ radios. Since 2004 it is Italy’s exclusive DAMM TETRA distributor. It held ~60% of the civilian TETRA market (350+ base stations) Access Data Shiraume Hospital www.shiraume.or.jp Iwata, Shizuoka, Japan N/A N/A N/A Locked, Exfiltrated Shiramume Hospital is a regional general hospital in Japan providing comprehensive inpatient and outpatient care. It offers services in internal medicine, surgery, emergency care, obstetrics/gynecology, and rehabilitation, supported by diagnostic imaging and laboratory facilities. Access Data Nippon Medical School Musashi Kosugi Hospital www.nms.ac.jp/kosugi-h Kosugimachi, Kawasaki, Japan N/A 100M 902 Locked, E…

Screenshot of the leak post

Leak screenshot for Nippon Medical School Musashi Kosugi Hospital

Sources

Victim sitewww.nms.ac.jp/kosugi-h
Leak posthttp://netrunrsb3bivj5gnwajzxlig5qkteb6edgthxj7fmsvhkzxtwfxwaad.onion/view/MusashiKosugi

Source

Indexed 2 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.