I currently have my late father in-law's Power PC G4 Desktop with OS 10.4.11. I backed up the files on an external hard drive and deleted them on the iMac.. I don't know if there is any demand for this item, but the question is if I either sell it or trash it, how do I securely permanently delete all files that cannot be recovered by anyone? Thanks in advance to anyone to those that can help me on this issue.