There is nothing particularly surprising to a computer scientist that
"deleted" data is not really gone; in fact, that's SOP for almost any
data storage system, including the OS itself, all databases I know of,
and probably many other email programs.
The suggestions given are about as useless against a real enemy (such
as the FBI) as a $5 padlock or a fifth amendment. There are commercial
programs you can buy, like Norton's "wipefile", that claim to do a more
complete job of erasing data from a disk by physically overwriting it
many times with different values, but even these can be overcome by a
sophisticated snoop. The only secure way to erase a hard disk is with
something like thermite.
-- Lee Daniel Crocker <lee@piclab.com> <http://www.piclab.com/lcrocker.html>