This is a test of commonsense. Complete the next sentence:

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