Abstract: The present invention relates to a system for authentication of an end user of a user station arrangement (10) requesting access to protected information, comprising access server means (20) and authentication means (30), the user station arrangement (10) supporting communication with the authentication means (30) over a first communication channel of a radio network (40). It further supports communication with the authentication means (30) over a second communication channel. The authentication means (30) are adapted to, at reception of a request for access to protected information from a user station arrangement (10), establish if the user station arrangement (10) is reachable over the first communication channel.