“Secure deletion involves the use of special software to ensure that when you delete a file, there really is no way to get it back again. When you “delete” a file for instance, by putting the file in your computer’s trash folder and emptying the trash you may think you’ve deleted that file. But you really haven’t. Instead, the computer has just made the file invisible to the user, and marked the part of the disk drive that it is stored on as “empty,” meaning that it can be overwritten with new data. But it may be weeks, months, or even years before that data is overwritten, and the computer forensics experts can often even retrieve data that has been overwritten by newer files. Indeed, computers normally don’t “delete” data; they just allow it to be overwritten over time, and overwritten again. The best way to keep those “deleted” files hidden, then, is to make sure they get overwritten immediately. Your operating system probably already includes software that can do this for you, and overwrite all of the “empty” space on your disk with gibberish (optionally multiple times), and thereby protect the confidentiality of deleted data. Examples include GNU Shred (Linux), Secure Delete (Mac OS X), and cipher.exe (Windows XP Pro and later).”
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