-Some machines can recover data that's been written over only one or two
times, however. That's where secure delete standards, such as the
Department of Defense 5220.22-M, come in. According to this
specification, overwriting the drive sectors three times with specific,
different characters constitutes one pass. Many experts recommend seven
such passes to render the data completely unrecoverable. But reading
data that has been overwritten by even the simplest shredders requires
expensive hardware, so unless you're worried about professional sleuths,
such thorough overwriting probably isn't necessary.-


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