1. Method of non-intrusively modifying an executable file (E) containing references (F 1, F 2, F 3 ) to functions located in at least one shared library (B) within a computer, characterised in that, in respect of a reference file in the executable file calling up a given function of the shared library, a reference file is accessed and acts as a link between the executable file and the location where said given function is actually located, the address of this given function being contained in this reference file, and this address is replaced by a new address pointing to another function so that calling up said function will enable this other function to be run whilst the executable file is being run.