In a small error in judgement you have downloaded some very unfortunate photos or files onto your phone or PC. Naturally you immediately delete it. But does it really ‘delete’? A while ago there was a scandal involving celebrities having revealing photos leaked; photos they long assumed were deleted.
The ‘hackers’ had simply made a program that tried every possible password combination. Such programs are readily available of the Internet. Apple also didn’t bother warning them that somebody was making a huge number of attempts to try and log in. Once they were on they recovered photos that were ‘deleted’.
First let’s examine how a hard drive works. Computers only understand 1s and 0s. Why? Because an electrical signal can only be high (1) or low (0). So how is information stored? The answer is magnets. Take an iron nail, it can be magnetised by rubbing a magnet over it. Imagine when it is magnetised it is 1 and when it is 0 it is demagnetised.
A hard drive contains billions of these ‘iron nails’ that store these 1s and 0s. A single ‘Iron nail’ in computing terms is called a byte. This is the unit electronic storage is measured in. For example an iPhone has typically 64 gigabytes of storage. That is 64,000,000,000 bytes.
So say you stored an image that was 1,000,000 bytes (1MB), the hard drive would allocate 1,000,000 of these bytes in the hard drive to store the 1s and 0s needed to form the image. Now when you delete the image, nothing happens to the actual information. Quite simply when you press delete, the hard-drive allocates the area for new information rather then removing it.
Imagine you have a file that can fit exactly 100 sheets of paper. You write on one page and decide to scribble it all out. Then rather than rip the page out, you simply move onto the next page. Now when you write on all pages, you remember that you don’t actually need the page you scribbled out. So you rip it out an replace it with a new, blank one. When you decided to ‘delete’ the piece of paper, you didn’t delete it. All you did was allocate that page to ‘replaceable’.
This is what a hard drive does, it allocates the bytes to ‘replaceable’. As in when you run out of space on the hard drive, that is when the hard drive will go back and overwrite old data.
That means that information with the right tools can be recovered, if the bytes haven’t yet been replaced. Back to the scandal, this is what happened. The information hadn’t been physically destroyed at all, it was still there, just hidden. The hackers recovered the images and thus celebrities were confused at how they had surfaced.
So how do you actually remove information? Logically destroying the entire hard drive would work, but even then there have been cases of hard drives being found in pieces and experts have found which bytes have a 1 and which have a zero, finding bits of information.
A working way is to fill the entire hard drive with garbage and overwrite everything. But it can prove difficult and requires a lot of time.
The fool proof way is to run a magnet over the hard-drive, magnetising the entire thing. It’s shown in the popular TV show Breaking bad. When Walter puts a huge magnet in the back of a van that wipes the information stored on a laptop in police custody. All the bytes are magnetised (so they are 1s) and therefore no information is stored.