You all know how to empty the Macintosh trash of the files you’ve dragged there. (Or used Command-Delete to trash) The Mac’s hard drive churns for just a second and the trash bin turns from a full icon to an empty trash icon. What really happens though? All computer operating systems that I’m aware of delete the files by removing the reference to them from the file directory, and marks that space on your hard drive as free space to write to again. It doesn’t really go out and erase every bit of the files. They are actually still sitting there on your hard drive. That is, until some other file writes over the top of them.
According to Apple’s web site, “That’s why Mac OS X Leopard provides another option for deleting data: the Secure Empty Trash command. Meant for those occasions when you want to permanently and immediately delete files, Secure Empty Trash overwrites your data with digital gibberish, ensuring that your deleted data is gone for good. It may take a few moments longer, but it’s a good choice for deleting data you’re sure you don’t need — and don’t want anyone else to see.
To delete your Trash securely, go to the Finder menu and select Secure Empty Trash. A pop-up will ask you to confirm that you want to permanently erase the items in the Trash. Click OK, and these files will be gone forever.”