This uses many overwrite passes, with the data patterns chosen to
maximize the damage they do to the old data. While this will work on
floppies, the patterns are designed for best effect on hard drives.
For more details, see the source code and Peter Gutmann's paper `Secure
Deletion of Data from Magnetic and Solid-State Memory'
(http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from the
proceedings of the Sixth USENIX Security Symposium (San Jose,
California, July 22-25, 1996).