Substack, a high-profile publishing platform widely used by academics, journalists, subject matter experts, and controversialists, has suffered a data breach affecting an unknown number of its creators and subscribers. According to emails sent out this week to some users, on February 3 the company “identified evidence” that a third party had exploited an unspecified weakness in the company’s systems to gain access to user email addresses, phone numbers and, more vaguely, “other internal metadata.” The breach happened in October 2025, which means that data, which the company said did not include credit card numbers, passwords, or financial information, has been exposed for up to four months. ...