Castle enables online businesses of all sizes to detect and prevent user account fraud, a technology previously only available to banks and large financial institutions. Whether you’re building a bitcoin service, e-commerce store, mobile app, or any other customer-facing application, Castle's API's lets you add account hijack protection. Castle tracks fraudsters based on device fingerprint, keystrokes, site browsing history, and hundreds of other signals. Whenever something suspicious occurs, both the administrator and account owner are alerted and can immediately take appropriate action.