It is claimed(by the paranoid), but not proven, that intelligence agencies could use magnetic force microscopes to reconstruct overwritten data and that therefore one would need to use multiple passes (such as the Gutmann method) to counter this. Of course, as someone? once said, "just because you're paranoid it doesn't mean that they're not out to get you."If the data was deleted after 1 pass why even have the 3, 7 or 35 passes and why is doing it multiple times great?