Originally posted by: n0cmonkey
Originally posted by: sciencewhiz
Originally posted by: drag
If your realy paranoid, do this:
dd if=/dev/zero of=/dev/hda
dd if=/dev/urandom of=/dev/hda
That will wipe everything from the MBR down to the last sector of the harddrive. It'll be as clean as you just bought it.
No, the drive will contain completely random data, with traces of your original data still magnetically present. The DoD requires 7 writes of specific bit patterns to erase the latent magnetic data. However, for really sensitive stuff, they physically destroy the platters, which means they don't even completely trust thier algorithms.
The DoD is behind the times. It's possible that traces will be present no matter what you do. All 0's, all 1's, and random 0's and 1's are the best bets for most people. (combination sof the three)
Just run it 7 times. Your done.
The problem is that there are variations in the head movement.
Now your already dealing with very small spaces, but because nothing is exact the designers of the harddrive have to make a little space between the successive lines of magnetic data. Just to take up the slop. If you have the head right data right next to each other, then you'd eventually have data migrating magneticly into the lines of data next to it. So they make a little space.
Now if data is on the disk for a long time, it will leave traces of magnitism on either side of were the data is written. So when you overwrite the data, a little bit of the magnitism from the original data is still existing in the channels of nothingness on either side. So if you want to recover this data you have to have a machine that is much more sensitive then the harddrive head itself... to read between the lines so to speak.
By writing over and over agian, it's hoped the successive writtings will overpower the residual stuff in the channel on either side of the data and obscure it enough to make recovering the original data recovery prohibitively expensive or technically impossible.
That's why I just urandom it. If I am paranoid I'll over write it with successive zeros and urandom data. That's about as you good as you can get.
If you want more protection, just use the best data wipe programs/devices America has to offer. A personal favorite of mine is the
Mossberg 500 data wipe machine. It's very reasonably priced at around 150-500 dollars depending on the condition and features, and it only costs pennys per use. Even comes with a wood grain finish if you want.
Although I will have to warn you that it may lower the retail value of your harddrive a bit.