The Sentry security incident on June 12th was triggered by a vulnerability in the backup infrastructure, which led to concerns about data leakage. The company immediately took action, revoking permissions and credentials for affected buckets, and rotating internal credentials. However, due to incorrect S3 ACL configurations, an attacker could have accessed sensitive user details, including bcrypt-hashed passwords, from backups. To address this, Sentry worked on a password expiration feature, which was completed in the afternoon, but was later polished up. The company also contacted affected partners and implemented measures to improve security, such as pre-encrypting backups prior to sending them to S3. As a result of the incident, Sentry has identified areas for improvement, including multi-factor authentication, encryption strategies, and additional security controls.