First, it does seem that a single pass with random data is enough to securely erase data. This was widely debated for quite a while (in the computer forensics community at that), but today all the literature I can find supports this, as far as modern hard drive platters are concerned anyway. However, there are two things to take into consideration A. Only parts of the drive that are overwritten are overwritten. This should go without saying. And there is a nice paper...somewhere (maybe I will dig it up later if nobody else has a link on hand) that discusses how normal hard drive wiping software (ie: with no firmware component) can not put the head off the center of the track, leaving magnetic residue that is not actually overwritten along the edge of the track. Even if a file leaves only trace amounts of magnetic residue after it is wiped, in some cases it could be enough to recover partial data (and in some cases partial data is all that is required to determine the entire file that was wiped if there is a reference, at least to a high probability, fuzzy hashing comes to mind). ATA secure erase has a firmware component that allows it to wipe off track center. B. Only parts of the drive that are overwritten are overwritten This should go without saying. And depending on your filesystem, you never really know where all traces of files are going to leak to. So even if you wipe the file itself, are you sure you wiped all remnants of it ? Probably not, unless you wipe the entire drive.