The invention relates to a method for authenticating a user accessing a remote server from a computer. The method comprises connecting to the remote server from the computer; logging into the remote server using a user-specific identifier; authenticating the remote server in the computer; sending an unpredictable message from the remote server to the computer; establishing communication between the remote server and a terminal belonging to the user; authenticating the remote server in the terminal; authenticating the terminal in the remote server; inviting the user to enter the unpredictable message in the terminal; using the terminal to send the message entered by the user in the terminal to the remote server; and if the message entered by the user in the terminal matches the unpredictable message, authenticating the user in the remote server.