Hacker claims theft of data from 700,000 Substack users; Company confirms breach

Securityaffairs.Co •Pierluigi Paganini • February 5, 2026

Substack confirmed a data breach after a hacker leaked data from nearly 700,000 users, including email addresses and phone numbers. Substack is an online platform for publishing email‑based newsletters and blogs, with built‑in paid subscriptions and basic analytics. It’s free to start; creators pay a fee on paid plans. In 2026 it’s estimated to serve […]

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Substack Breach Exposes User Emails and Phone Numbers from October Hack Substack has disclosed a security breach that exposed user email addresses and phone numbers due to a hack that occurred in October 2025. The breach went undetected for four months, with CEO Chris Best confirming that no passwords, credit card information, or financial data were compromised. Users were notified on February 3, 2026, but details about the number of affected users and the technical specifics of the vulnerability remain undisclosed. 30 sources 43

Hacker claims theft of data from 700,000 Substack users; Company confirms breach

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