Hi Youngnobody,

Not meaning to hi-jack your parade, but they work slightly different to how you described.

They don't encrypt the data several times, they simply overwrite the data with random data, several times over, (I think 7 times is the standard for completely obliterating data short of destroying the drive) before then deleting that section.

The reason for this is that like you said, if you simply just delete that data, it is still there, just the index entry to it is deleted. Even if you overwrite that physical section of the hard disk once or twice, some of the data can still be restored. After seven new writes to that section the data is considered totally gone with almost nothing left (although i'm sure there are some advanced and VERY expensive techniques to recover it though)