For what it's worth regarding multiple passes to sanitize data:
http://www.infosecisland.com/blogview/16130-The-Urban-Legend-of-Multipass-Ha...
http://cs.harvard.edu/malan/publications/pet06.pdf
On Thu, Oct 4, 2012 at 5:06 PM, Seth David Schoen
I was also concerned by the "Securely Destroying Data" section. Although it acknowledges some situations under which erased data (or even overwritten data) could be recovered, it seems to treat these situations as exceptional and multiple-overwrite tools generally reliable. It doesn't mention that these tools are potentially quite untrustworthy on current filesystems even under normal conditions, because of data journaling. (I first learned about this problem from John Gilmore.) In fact, even the man page for shred gives a warning about this:
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