Method for authenticating a user to a central server and using a selected one of several electronic devices (120,122,300,400,500,600), which electronic devices each comprises a screen display (121,123,310,410,510,610) and are arranged to communicate with the central server, wherein the method comprises the steps a) associating, in the central server, each of the electronic devices and/or each of a set of registered users, with a respective unique set of different digitally stored codes, known to both the electronic device in question and to the central server, and associating each individual code with a certain piece of information in a predetermined set of information pieces, so that the data provided from the electronic device (120, 122) to the central server will depend on the identity of the actual device (120, 122) used for authentication; b) providing a software function, accessible from the selected electronic device in an individualized way, in the sense that the software function is provided access to unambiguous information regarding the identity of the electronic device itself in connection to such access; c) causing the software function to provide, on the said screen display of the selected electronic device, a graphical user interface comprising a user control which can be activated in several different ways, where different ways of activation are associated with different respective codes selected from said unique set of codes for the selected electronic device and/or the user; d) allowing the user to specify at least one piece of information by activating the user control in the corresponding respective way, and determining the corresponding at least one associated code; e) calculating an output value of a predetermined one-way function, to which the said determined at least one code is used as input value; f) communicating the calculated output value from the selected electronic device to the central server; g) causing the central server to calculate a comparison output value of the said one-way function, using as input values the respective codes having been associated, in step a), with a certain expected set of information pieces which the user is expected to have specified in step d); and h) authenticating the user if the calculated comparison output value equals the calculated output value, and in that the central server identifies each individual electronic device using a respective individualized local presence of the said software function on the electronic device in question or using a hardware serial number of the electronic device. a) associating, in the central server, each of the electronic devices and/or each of a set of registered users, with a respective unique set of different digitally stored codes, known to both the electronic device in question and to the central server, and associating each individual code with a certain piece of information in a predetermined set of information pieces, so that the data provided from the electronic device (120, 122) to the central server will depend on the identity of the actual device (120, 122) used for authentication; b) providing a software function, accessible from the selected electronic device in an individualized way, in the sense that the software function is provided access to unambiguous information regarding the identity of the electronic device itself in connection to such access; c) causing the software function to provide, on the said screen display of the selected electronic device, a graphical user interface comprising a user control which can be activated in several different ways, where different ways of activation are associated with different respective codes selected from said unique set of codes for the selected electronic device and/or the user; d) allowing the user to specify at least one piece of information by activating the user control in the corresponding respective way, and determining the corresponding at least one associated code; e) calculating an output value of a predetermined one-way function, to which the said determined at least one code is used as input value; f) communicating the calculated output value from the selected electronic device to the central server; g) causing the central server to calculate a comparison output value of the said one-way function, using as input values the respective codes having been associated, in step a), with a certain expected set of information pieces which the user is expected to have specified in step d); and h) authenticating the user if the calculated comparison output value equals the calculated output value,