"I used to think a simple format of a hard drive was enough to
make data recovery impossible, but I was wrong. To ensure that
details of your secret love affair, bank account passwords, and
daily porn site visits cannot be recovered, use shred.
"Deleting a file with the rm command merely adds a file's data
blocks back to the system's free list. A file can be restored
easily if its 'freed' blocks have not been used again. shred
repeatedly overwrites a file's space on the hard disk with random
data, so even if a data recovery tool finds your file, it will be
unreadable. By default, shred does not delete a file, but you can
use the -u or --remove switch to delete it..."