Once a file has been deleted, it never really disappears from the system and in fact can still be accessed. If a file is moved to the trash, it doesn’t mean it has actually deleted and even when the trash is emptied, the space inhabited by the file isn’t actually emptied.
When a file is ‘deleted’ from the system and then from the trash, it is simply marked ‘empty’. Michael explained the process and said that the file itself hasn’t actually moved out and only the pointers have gone away. The pointers are a kind of data that point to places in a computer’s memory where the file a user is referencing can be found, and therefore ‘overwriting’ the file is needed to make it unrecognizable. Even overwriting at times doesn’t work as there have been instances where hackers were able to put back the information together even after the file was overwritten for more than 35 times. So, there is nothing is permanently deleted and the best way to keep the data safe is to keep the hard drives of your old computers before ditching, donating or selling it.