I have a few “dead” hard drives from old computers - I used to build computers. These have given up the ghost and I just kept them because they potentially have sensitive data on them. Because they don’t operate any more, I can’t use software to wipe them. What is the best way to make sure that data can’t be read off these drives by the casual hacker. I am not worried about the NSA (they probably know everything already). I suppose I could take a hammer to the drives, but that seems a bit harsh.