[header] How to securely wipe an imac or mac os x based system hard drive [title] Boot an imac or apple-based higher system. [title] Make sure you've backed up all your necessary data to a thumb or external hard drive. [step] This data includes important documents, media, itunes files, and bookmarks. 
[title] Safely remove this thumb or external hard drive so that it is no longer connected to your system. [title] As a precaution, physically detach all connected disks that you do not wish to wipe.