Originally posted here by xierox
I recommend writing random bits to the entire drive more than once as a simple way to make data very hard to recover. Check out DBAN (Darik's Boot and Nuke) for your wiping needs. I think it will fit the bill nicely.
Of the five different wipe methods it offers, it has at least one that meets the American DoD 5220-22.M Standard Wipe requirements. (Features.)

- X
I also recommend DBAN, as someone who's used it and subsequently verified that the wipe was complete.

The one drawback to DBAN, as I understand it, is that it can't yet deal with Host Protected Areas on disks. You'll need to remove the HPA setting first, before the wipe. Supposedly, this is an issue that will be addressed in an upcoming version of DBAN.