Quote from AndroidXP :

Kinda like this:

Interesting; thanks.

What would be the effect of overwriting with all 1's? Would the previous data be detectable, in that case?

Yes, you'd notice a slight (although in that [not entirely accurate] example less visually apparent) difference to where the zeros were. But once you overwrite it with random data once or twice you can pretty much consider it gone for good, unless someone REALLY wants to spend ridiculous amounts of money on reconstructing it.

Quote from AndroidXP :

Yes, you'd notice a slight (although in that [not entirely accurate] example less visually apparent) difference to where the zeros were. But once you overwrite it with random data once or twice you can pretty much consider it gone for good, unless someone REALLY wants to spend ridiculous amounts of money on reconstructing it.

... and even then, the data you recover is likely to be incredibly fragmented, and certainly not reliable enough to trust - as by that point, you're not entirely sure which particular write left the residue