Reply #15: you are absolutely bang on the money

[McKenzie]

third part uitilities such as "Filerecover" rely on the sectors the file resides on not being overwritten.

After a thorough overwrite magnetic analysis can still recover data but at huge cost. Criminals use a process known as "degaussing" to foil detailed analysis of HDD's and removeable media.

For you and I, overwriting to DoD standard is fine, particularly if random characters are used.