Why is permanently deleting a file without any trace of it left on the system is considered to be a really complicated process?

Question

I got the basics. Deleting a file simply tells the system that the sectors it occupied are now available for new data to be written on.

But if you want a more secure deleting why cannot you just overwrite everything with zeroes? If the computer system is only working at its core by manipulating zeroes and ones, why is it said that physically destroying the drive the information is stored on, is the only secure way to make sure nothing is left on it?

In: Technology

Answer 1

Imagine you have a wall painted white, and you paint a message in black. Even if you put a new coat of white paint, it’s still possible to see where were the black parts, because the coat of white paint is not thick enough to hide everything.

With a hard drive (let’s use the typical HDD), something similar happens. Zeroes and ones are a specific amount of “magnetic charge”, with some tolerance for variation. But if you overwrite everything with zeroes, the previous charge is not lost, you’ll find that where there was a zero, the charge is low, and where there was a one, the charge is higher (still below the threshold for zero, but high nonetheless). With the correct equipment, it’s possible to retrieve the deleted information.

You would need to overwrite the deleted information with random digits several times.