Do I have a responsibility to turn these people in? I know some/many/most of the users are grey/black hats. I might even have a notion of who those people are.
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Let's flip the argument a wee bit. Say you're working for a weapons contractor building simulators and other tools for drones & ICBMs. You have a pretty good idea that your work is being used for death and destruction. You see some videos on the evening news of some people getting killed by a drone you helped build. Do you bear responsibility for the use of that drone?
Because I see the answer to both to be about the same.