MalwareHealthcareHealthcareRansomwareData ExfiltratedData EncryptedRansom DemandedIdentity (basic)Government IDHealth (basic)PHIMediumContained

Horizon Behavioral Health

bd_ba25fb5419d6a006 · schema v1 · pii pii-v1

Severity

Medium

Discovered

Mar 16, 2025

Filed

Apr 21, 2025

To disclose

5 weeks

Affected

6state residents only

Linked

5 filings

Confidence

63%

Full breach record for Horizon Behavioral Health →

Horizon Behavioral Health notified Montana residents of a ransomware incident discovered on March 16, 2025, with unauthorized access occurring between March 13 and 16, 2025. The breach impacted PHI, including clinical information, and PII such as SSNs and driver's license numbers. Horizon engaged forensic experts, notified law enforcement (FBI, CISA), and provided complimentary identity monitoring to affected individuals.

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Incident timeline

undetected · 3 days

discovery → filing · 5 weeks / 36 days

Mar 13, 2025

Begins

Mar 16, 2025

Discovered

Apr 21, 2025

Filed

vs. sector median

7 wks faster

This filing is one of 5 about the same incident.View merged incident

Linked disclosures

Why this link?

Regulatory filings (4) · sorted by filing gap

Vermont State AGbd_225fc4e0b0d887932025-04-21Candidate
Nebraska State AGbd_494ebdd5f2841ce42025-04-21Verified
HHS OCRbd_87431939e0eabf122025-04-21Candidate
Massachusetts State AGbd_c52606e3518997232025-04-21Verified

Name: Horizon Behavioral Health
norm: horizon behavioral health

Name: Horizon Behavioral Health
norm: horizon behavioral health
Industry: Healthcarellm

Discovered: Mar 16, 2025
Breach occurred: Mar 13, 2025 – Mar 16, 2025
Undetected for: 3 daysoccurrence → discovery
Materiality determined: —
Notification sent: —
Affected individuals: 6state-resident count only
Data types: Identity (basic)Government IDHealth (basic)PHI
Data elements: Social Security numberDate of birthMedical information
Attack vector: Ransomware
MITRE ATT&CK: T1486 Data Encrypted for ImpactT1041 Exfiltration Over C2 Channel
Threat actor: ExternalFinancial
Regulator citations: Notified FBI’s Cyber Crimes DivisionNotified Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA)Notified Cyber Fusion Center of the Virginia State Police

During the incident: Took steps to stop the ransomware
Engaged outside cybersecurity experts to investigate this event
Notified state and federal law enforcement, including the FBI’s Cyber Crimes Division, the Department of Homeland Security’s Cybersecurity and Infrastructure Security Agency (CISA), and the Cyber Fusion Center of the Virginia State Police
Arranged to provide complimentary identity monitoring for any individuals with data potentially implicated by this incident
Reviewed our system security and taken steps to increase that security going forward
Changes made: Continuing to evaluate additional actions to strengthen our network security
Taken steps to increase that security going forward
Source: Quoted from the filing itself, not independently verified.

Time to disclose: 5 weeks(36 days from discovery to filing)
Compliance flags: — (clock not assessable for this source)

Status: No extraction artifact recorded for this disclosure.

Filing propagation · 5 filings · 5 states

View merged incident ↗

Vermont State AGApr 21 · first

Nebraska State AGApr 21 · first

HHS OCRApr 21 · first

Massachusetts State AGApr 21 · first

Montana State AGApr 21 · first · this page

Evidence ladder

Leak-site claim

Attacker assertion only. Establishes: claim date, group, alleged victim.

Press / market report

Unlocks: incident narrative, operational impact. Still no compliance clock.

State AG / regulator filingThis record

Unlocks: discovery date, data types, affected count, compliance clock.

SEC 8-K / victim statement

Unlocks: materiality, stated response, full audit trail. Ceiling removed.

Source URL: https://dojmt.gov/wp-content/uploads/2025/12/Consumer-notification-letter-1.pdf
DisclosureLens links to the originating regulator URL — full filing bodies are not redistributed from public surfaces (§4.5).
Filed at: Apr 21, 2025
Raw hash: 1ecccaec524a0909a881d95224da05bedfdc1dac5fc9fc2977d1a40f8f7f6e5d

Linked disclosures

Regulatory filings (4) · sorted by filing gap

Reporting entityHorizon Behavioral Health

Victim entityHorizon Behavioral Health

Incidentdiscovered Mar 16, 2025

Stated responseTook steps to stop the ransomware

Complianceclock not assessable

Extraction provenanceno artifact recorded

Source provenancedojmt.gov