Newsletter platform Substack has confirmed a data breach in an email to users. The company said that in October, an “unauthorized third party” accessed user data, including email addresses, phone numbers, and other unspecified “internal metadata.”Substack specified that more sensitive data, such as credit card numbers, passwords, and other financial information, was unaffected. In an email sent to users, Substack chief executive Chris Best said that the company identified the issue in February that allowed someone to access its systems. However, the company asked users to take caution with emails and texts without any particular indicators or direction. On its website, Substack says that its site has more than 50 million active subscriptions, including 5 million paid subscriptions — a milestone it reached last March.