Nippon Medical School Musashi Kosugi Hospital Listed by netrunner Ransomware Group: Ransomware Claim — What’s Alleged & What To Do

On April 3, 2026, the netrunner ransomware group listed Nippon Medical School Musashi Kosugi Hospital on its leak site, claiming that internal files had been taken during a ransomware incident. The number of individuals whose information may be involved remains unknown, and no further details about the scope or confirmation of the listing have been made public. The incident matters because the hospital is a 372-bed regional teaching facility that handles emergency, critical care, perinatal, pediatric, cancer, and other sensitive services for the Kawasaki area. Any exposure of internal records from such an institution can affect patients, staff, and the continuity of care even when the precise contents of the claimed exfiltration are still undisclosed.

Inside the incident

Public information is limited to the April 3, 2026 listing by the netrunner group, which asserts that internal files were exfiltrated in a ransomware attack. No official statement from the hospital, no confirmed count of affected records or individuals, and no timeline for the underlying intrusion have been released. The method of initial access and the extent of any encryption or data removal also remain undisclosed at this time.

Inside netrunner

Netrunner is a ransomware operation that maintains a public leak site to list organizations it claims to have targeted. The group typically conducts double-extortion attacks, first encrypting systems and then threatening to publish stolen data if a ransom is not paid. Its listings are presented by the group itself and are not independently verified in every case. Prior public reporting has associated the actor with healthcare and other critical-infrastructure targets, though specific claims regarding Nippon Medical School Musashi Kosugi Hospital originate solely from the April 2026 listing.

Nippon Medical School Musashi Kosugi Hospital and its sector

Nippon Medical School Musashi Kosugi Hospital is a 372-bed regional teaching hospital in Nakahara-ku, Kawasaki, affiliated with Nippon Medical School and established in 1937. It operates 36 clinical departments that include emergency and critical care, an ICU, NICU, perinatal and pediatric services, cancer treatment, and minimally invasive procedures. The facility functions as a regional hub with disaster-resistant infrastructure and an on-site heliport, supporting both patient care and medical education.

Healthcare organizations of this type routinely process large volumes of clinical, administrative, and research data. A claimed compromise at a teaching hospital therefore intersects with both immediate patient services and longer-term institutional functions.

What data was at risk

The only detail released is that internal files were claimed to have been exfiltrated. No inventory of specific record types, patient counts, or file categories has been published. Hospitals of this scale typically hold electronic health records, laboratory results, imaging studies, billing information, staff credentials, and research or operational documents. The exact contents of any material listed by the group are unconfirmed.

What's at stake

For individuals whose records may be among the claimed files, the primary concerns are unauthorized access to medical histories, potential misuse of personal identifiers, and secondary effects such as insurance or identity fraud. For the hospital, the incident raises questions about operational continuity, regulatory obligations, and the protection of data that supports both clinical care and teaching activities. Because the number of affected people and the precise nature of the files remain unknown, the full extent of these risks cannot yet be quantified from public sources.

Were you affected?

Begin by contacting Nippon Medical School Musashi Kosugi Hospital directly for any official notifications or guidance it may issue. Monitor statements from the hospital and relevant Japanese data-protection authorities for updates on the incident. Individuals can also run a free exposure scan of their email address against known breach data sets to check whether their information appears in previously published leaks.

AICompiled with AI assistance from public sources and published under our editorial standards.