The invention relates to a security token comprising a communication interface adapted to communicate with a host computer; a security module, comprising encryption based security features; and a non volatile memory storing at least an application to be uploaded and executed in a host computer. The application makes use of the security features when executed in a host computer in communication with the communication interface. The security token is adapted to modify the content of the application as uploaded or its execution parameters at successive connections of the security token to a host computer.