You can't do much

Once you make some piece of knowledge public, you cannot help to stop it from spreading. Public computer software is public knowledge. What others do with your software shouldn't be your concern. This applies to any other product such as kitchen knives or gaffer tape; you can use a kitchen knife to inflict damage upon a person or you can use gaffer tape to unlawfully restrain someone against their will. This also applies if someone takes some code from your program to do something pretty nasty such as using it as part of a nuclear missle program - because when the actions of the other parties reaches this stage of moral ambiguity, it is assumed that these issues also become the interest of national and international bodies which will take actions that will deal with the situation.