SMSAuthenticator is an authentication module for situations where "username and password"-login provide insufficient security. The additional security is achieved by sending keys (single-use passwords) by SMS to the user's mobile phone. It solves some of the main problems with ordinary passwords (e.g., password guessing and password sniffing) without requiring special hardware on the user's side. It is a Java-based (J2SE 1.2 or higher) Web service using SOAP for communication. It also requires a database with JDBC support (tested with PostgreSQL).