Disclosure context

About Cloak

Cloak is a relatively new ransomware group that emerged in August 2023, operating with primarily financial motivations and demonstrating a broad international targeting scope with 162 documented victims across multiple sectors. The group's origin and specific affiliations remain undocumented in public threat intelligence reporting, though their operational patterns suggest they may operate independently rather than as part of a larger ransomware-as-a-service ecosystem. Limited public documentation exists regarding their specific attack methodologies, encryption techniques, or data exfiltration practices, though their targeting patterns indicate sophisticated capabilities to compromise organizations across diverse sectors including business services, technology, healthcare, and manufacturing. The group has demonstrated a preference for targeting victims in English-speaking countries and Western Europe, with the United States, Germany, United Kingdom, Canada, and Italy representing their primary geographic focus areas. Cloak appears to remain active as of current reporting, though the relative scarcity of detailed public analysis from major threat intelligence firms suggests either operational security effectiveness or a lower profile compared to more established ransomware operations. The group has been linked to 162 public disclosures across our corpus. First observed on a leak site on August 24, 2023; most recent post February 24, 2026. The operation is currently active.

Timeline of this disclosure

September 7, 2025TuftsMedicine listed by Cloakon 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, TuftsMedicine is reported in United States, a country with 7,392 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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TuftsMedicine

Claimed by Cloak · listed 9 months ago

Age

since listed · data leaked

Status timeline

Listed
Sep 7, 2025
Data leaked

At a glance

Group: Cloak
Status: Data leaked
Country: United States
Sector: Healthcare
Listed on leak site: Sep 7, 2025

About the victim

AI dossier — public-source company profile

Tufts Medicine is a not-for-profit integrated health system based in Boston, Massachusetts, serving patients across eastern Massachusetts. The system includes Tufts Medical Center, Lowell General Hospital, MelroseWakefield Hospital, and affiliated community care networks. It operates as one of the region's major academic medical systems with thousands of physicians and staff.

Industry: Healthcare & Hospital Systems
Address: 800 Washington Street, Boston, MA 02111, United States
Employees: 10000+
Founded: 2022

Attack summary

Severity: critical — Tufts Medicine is a large academic healthcare system; data_published status strongly implies confirmed exfiltration of protected health information (PHI) and PII at scale, which constitutes regulated medical data under HIPAA — meeting the critical threshold.

The Cloak ransomware group claims to have attacked Tufts Medicine and has listed the disclosure status as data_published, indicating data was exfiltrated and subsequently published. The specific categories and volume of data published are not described in the available leak post excerpt.

critical

Data the group says was taken

AI dossier — extracted from the leak post

Patient records
Personally identifiable information (PII)
Protected health information (PHI)
Employee data
Financial records
Internal business documents

Original description

AI-summarised, not from the leak post

N/A

Sources

Victim sitetuftsmedicine.org

Source

Indexed 9 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.