Hacker claims theft of data from 700,000 Substack users; Company confirms breach
ID: df435d50-832b-5497-be98-fa2821a8f283
STIX ID: report--df435d50-832b-5497-be98-fa2821a8f283
Feed Name: Security Affairs
Threat Score
Substack confirmed a breach that exposed email addresses, phone numbers, and internal metadata for nearly 700,000 users (incident occurred October 2025, discovered February 3, 2026); the company says passwords and financial data were not accessed, is investigating, and is taking steps to improve security after a threat actor claimed the data was leaked on a cybercrime forum.
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