Abstract: A method for real-time authentication or authorization of a user (1) of a secured system (3) is based on using two authentication channels and an authentication device (4) from which the secured system can request authentication or authorization (6) over a secured information network connection (6, 9). One of the authentication channels is a telephone network (8), to which the authentication device (4) is connected. A user logging into the secured system (3) over the other channel (6) of the authentication channels must make a call to the authentication device over the telephone network by his or her telephone (2). The authentication device verifies that a call has been received from a telephone number of the user's telephone, and issues a positive verification response to the secured system. Upon receiving a positive response, the secured system provides a requested service through the other channel.