Overwriting Magnetic Data

Magnetic media present a special problem for those trying to protect the contents. When data are stored on magnetic disks, the ERASE or DELETE functions often simply change a directory pointer to free up space on the disk. As a result, the sensitive data are still recorded on the medium, and they can be recovered by analysis of the directory. A more secure way to destroy data on magnetic devices is to overwrite the data several times, using a different pattern each time. This process removes enough magnetic residue to prevent most people from reconstructing the original file. However, “cleaning” a disk in this fashion takes time. Moreover, a person using highly specialized equipment might be able to identify each separate message, much like the process of peeling off layers of wallpaper to reveal the wall beneath.