Drive Help

Hey, /g/. I was doing some work on a friend's computer which required a reformat of their hard drive. I backed up all of their files to a spare drive I had, and reformatted their original. After copying all the files back (after various virus scans, etc.) I'm still left with their files on my spare drive. My friend has asked me to delete the backup, because they have some personal/legal documents inside. I obviously have no use for anything on it, and I want to make sure the stuff is totally gone, as my friend is a bit paranoid.

Will using DBAN and zeroing the drive allow me to reformat it and use it like normal again, minus the files? I plan to use the spare drive for more backups in the future, but I still want my drive to work. What's the best way to completely erase the files but still use the drive later?

If you want to make absolutely sure no one ever reads those personal/legal documents, thermite.

http://hackaday.com/2008/09/16/how-to-thermite-based-hard-drive-anti-forensic-destruction/

Current government standards require that a magnetic disk drive be overwritten 21 times depending on the information.  To get anything past a few rewrites I think you need special hardware...  Do 7 to 15 passes and you should be in the clear and still have a workable hard drive.  One pass is good enough, unless you've got nerdy enemies or are selling it on e-bay.