Wiping your disk drive clean
 

Everybody who owns a computer will someday need to dispose of a disk drive. Before you do, it is a good idea to cleanse the drive, so no one can read your sensitive information. Deleting files and reformatting is not sufficient; determined effort can still reveal data from a drive even after it appears to be gone. To do a more thorough job, I suggest using wipe.

You need to take special pains because files that are "deleted" are not really gone. Most operating systems, including Linux and its ext2 filesystem, just delete the pointer to a deleted file; the data still exists on the drive. It is not effectively removed until every bit of the space it was occupying on the drive has been overwritten. Even then there are ways, albeit difficult, to analyze the drive and extract data. The only way, short of melting the drive, to ensure the data is gone for good is to overwrite the drive several times with random data.

http://www.linux.com/feature/135944

"Wipe" works nicely:)