Originally Posted by abelenky

On this point, I disagree. Once data has been overwritten once, it becomes very difficult to recover; essentially you'd just be looking for a weak "shadow" signal of the previous magnetic bit.

Once data has been overwritten 4 or more times, it is absolutely impossible to figure out what was there before. And most off-the-shelf data wiping tools will do multiple overwrites.

If there is any source/evidence that a government agency can recover data that has been specifically wiped, I'm willing to listen. But short of that evidence, the idea goes against everything i know about hardware, software, and physics.