A simple magnet won't work to erase data if someone has tools to get it. What is needed is a very strong electromagnet running a degaussing routine... degaussing involves a frequent 180 degree field reversal with a declining strength. The key is to randomize all the bits many time over. A unidirectional magnet will put the bits in one direction, but by reading the relative strength of the bits, the data can be reconstructed with ease.
Doesn't being constantly awakened all through the night have thhe same effect on the human mind?
Yep...see my other post.