This record tracks a ransomware attack claimed by the
shinyhunters group against
HMH (hmhco.com). It collects the publicly disclosed attack details — sector, location and
timeline — as published on the operator's leak site and indexed by Breach House.
Window Zero
EXPOSURE GAP
Window Zero is the time the breach stayed in the open before
anyone said so — the gap between when the attack was first discovered
on the operator's leak site (t1) and when it was publicly disclosed (t2).
The wider this window, the longer victims, staff and customers were exposed with no warning.
49days
t1 · Published
t2 · Disclosed
Business Category
Education
Disclosed / Notified
Aug 26, 2025
Attack Summary
[AI generated] HMH, or Houghton Mifflin Harcourt, is a long-established publishing company specializing in educational content. They provide a variety of instructional technology, assessments, and other learning materials to schools in over 150 countries. The company also publishes a number of well-known trade and reference works, alongside children's books. Their goal is to foster a lifelong love of learning in every individual they serve.
Leak Screenshots
SAMPLE
Proof-of-breach screenshots the operator posted from the stolen data. Previews are
redacted and locked — the originals are available on HaveIBeenRansom.
Dark Web Exposure
Findings for hmhco.com
— indexed by HaveIBeenRansom.
7,511
found in Infostealer logs
2,791+
found in Traditional breaches
209+
found in Ransomware leaks
Apollo.io DB 816millions.rar
Database World ROC · breach
••• emails
pureincubation-com.7z.001
Database World ROC · breach
••• emails
limeleads_breach.7z
TheUnderground - Reborn · breach
••• emails
@BreachedData1 LinkedIn 2021-23 Cleaned.7z.001
Database World ROC · breach
••• emails
VerificationsIO_BF.7z.011
Kedr | Forum · breach
••• emails
Televerde
play · ransomware
••• emails
New York Sports Club
play · ransomware
••• emails
linkedIN_2.7z.001
Database World ROC · breach
••• emails
+ 17 more leak sources locked
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Legal Disclaimer:
This ransomware victim record reflects information published on the operator's leak site.
Breach.house does not acquire, download, host, access or redistribute unlawfully obtained data. It indexes only publicly visible information posted by ransomware, breach and infostealer operators and open web sources, without accessing the underlying stolen content. The service supports public awareness, legitimate research and cyber-resilience.