MalwareEducationEducationRansomwareData ExfiltratedData EncryptedIdentity (basic)LowContained

Mastery Charter High School

bd_ac760a429f740ea3 · schema v1 · pii pii-v1

Severity

Low

Discovered

Sep 15, 2024

Filed

Jun 6, 2025

To disclose

38 weeks

Affected

Not disclosed

Linked

4 filings

Confidence

65%

Full breach record for Mastery Charter High School →2 incidents on file

Mastery Charter High School experienced a cybersecurity incident in September 2024 involving malicious encryption attributed to an unauthorized actor. The incident resulted in data exfiltration and affected personal information including names. The school shut down systems, engaged cybersecurity professionals, reported to federal law enforcement, and offered credit monitoring to affected individuals.

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Vermont clock✗ VT AG >45 bday38 weeks discovery → filing

⚠ unattributedNo provenance was recorded for this discovery date and it matches no other date on the record. It may be correct, but it is not independently grounded.

Incident timeline

undetected · 14 days

discovery → filing · 38 weeks / 264 days

Sep 1, 2024

Begins

Sep 15, 2024

Discovered

Jun 6, 2025

Filed

vs. sector median

+29 wks slower

This filing is one of 4 about the same incident.View merged incident

Linked disclosures

Why this link?

Regulatory filings (3) · sorted by filing gap

Indiana State AGbd_557cf3225408f29a2025-06-06Verified
Maine State AGbd_d445c07723535b6b2025-06-06Candidate
New Hampshire State AGbd_e77dfb9a7798647d2025-06-12 · +6dVerified

Name: Mastery Charter High School
norm: mastery charter high school

Name: Mastery Charter High School
norm: mastery charter high school
Industry: Educationllm

Discovered: Sep 15, 2024
Breach occurred: Sep 1, 2024 – Sep 15, 2024
Undetected for: 14 daysoccurrence → discovery
Materiality determined: —
Notification sent: Jun 6, 2025
Affected individuals: Not disclosed
Data types: Identity (basic)
Attack vector: Ransomware
MITRE ATT&CK: T1486 Data Encrypted for ImpactT1041 Exfiltration Over C2 Channel
Threat actor: ExternalFinancial
Regulator citations: reporting the matter to federal law enforcementreporting this Incident to relevant government agencies

During the incident: Proactively shutting down systems
Reporting the matter to federal law enforcement
Engaging experienced cybersecurity professionals to assist
Offering complimentary access to Experian IdentityWorks
Changes made: Expanding our current use of multifactor authentication
Implementing additional endpoint detection and response monitoring
Source: Quoted from the filing itself, not independently verified.

Time to disclose: 38 weeks(264 days from discovery to filing)
Compliance flags: VT AG >45 bday
Discovery-date grounding: unattributedNo provenance was recorded for this discovery date and it matches no other date on the record. It may be correct, but it is not independently grounded.

Status: No extraction artifact recorded for this disclosure.

Filing propagation · 4 filings · 4 states

View merged incident ↗

Indiana State AGJun 6 · first

Maine State AGJun 6 · first

Vermont State AGJun 6 · first · this page

New Hampshire State AG+6d

Pattern: first filing Jun 6 (IN), last Jun 12 (NH) — a 6-day rolling notification. Rolling spreads often mean counsel is filing as thresholds trip per state. Why this link?

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://ago.vermont.gov/document/2025-06-06-mastery-charter-high-school-data-breach-notice-consumers
DisclosureLens links to the originating regulator URL — full filing bodies are not redistributed from public surfaces (§4.5).
Filed at: Jun 6, 2025
Raw hash: d0fcc0bb28d724482687353a9be2391eec3019cee8363267ea022396b2b735d6

Linked disclosures

Regulatory filings (3) · sorted by filing gap

Reporting entityMastery Charter High School

Victim entityMastery Charter High School

Incidentdiscovered Sep 15, 2024

Stated responseProactively shutting down systems

ComplianceVT AG >45 bday

Extraction provenanceno artifact recorded

Source provenanceago.vermont.gov