Facebook announced that it kept hundreds of millions of Facebook users’ passwords “stored in a readable format” within its internal data storage systems in a press release today. Facebook said it has already fixed the error. Although the passwords were not exposed to anyone external to Facebook, the company said its login systems were designed to mask passwords to make them unreadable, particularly through a function called “scrypt” and cryptographic keys. Most of the compromised passwords were from users of Facebook Lite, a version of the platform used mostly by people in regions with lower connectivity. In addition to Facebook users, Facebook also said that tens of thousands of Instagram users also had passwords stored in a readable format.