the present invention is generally directed to a method , system , and article of manufacture that ensures the integrity of programs having variable portions . one aspect of this invention is a method for protecting software products having variant portions . this method includes identifying a reference to an external target in a software product , creating an identifier for the external target , and adding the identifier to the reference . in some embodiments , the unique identifier is a digital signature and the reference to an external target is a call to an external library .