Originally Posted by
Keith99
A single overwrite may not be enough. It can be possible to determine the previous value of each byte. Costly, but possible. After about 5 overwrites it is no longer possible (last time I heard).
I believe the DOD standard is 7 overwrites, the European standard is I believe now 20. And if it is an email you might as well not bother since they are not secure, and generally there is one residing on some server someplace. The key is not formatting it is overwriting preferably with random data I believe.
Also if you have stuff you don't want people to find I would start be putting it on an encrypted part of the drive, with only a password you know. Then when you want to get rid of it comes all the overwrites.