The invention relates to a method for secure piecemeal execution of a program code. In the method, the program code is split to a number of pieces in a first electronic device. The pieces are provided one after another to a second electronic device, which computes a message authentication code from the pieces and returns the authenticated pieces back to the first electronic device. In order to execute the program, the authenticated pieces are provided for execution to the second electronic device, which verifies the message authentication codes in the pieces to allow the execution of the pieces in the second electronic device.