Three ways of removing information from your computing devices, from the least effective to most effective, are deleting, overwriting, and physically destroying the device holding your information.
Deleting information is not effective. It removes pointers to information on your computer, but it does not remove the information. Do not rely on the deletion method you routinely use when working on your computer moving a file to the trash or a recycle bin, or choosing “delete” from a menu. Even if you “empty” the trash, the information is still there. It can be retrieved.
Overwriting is effective on all computing devices. It puts random data in place of your information, which cannot be retrieved because it has been obliterated. While experts agree on the use of random data, they disagree on how many times you should overwrite to be safe. While some say that one time is enough, others recommend at least three times, followed by “zeroing” the drive (writing all zeroes).
Physical destruction is the ultimate way to prevent others from retrieving your information. Of course, you should physically destroy the device only if you do not plan to give it to someone else.
Specialised services will disintegrate burn, melt, or pulverize your computer drive and other devices. If for some reason you do not wish to use a service, it is possible for you to destroy your hard drive by drilling nails or holes into the device yourself or even smashing it with a hammer. Fisher’s article, listed in “Further Reading,” contains more details. Fisher also warns to never burn a hard drive, put it in the microwave, or pour acid on it.
Some shredders are equipped to destroy flexible devices such as CDs and DVDs. If you smash or shred your device yourself, the pieces must be small enough that your information cannot be reconstructed; 1/125” is ideal.
Magnetic devices, such tapes, hard drives, and floppy diskettes, can be destroyed by degaussing exposing them to a very strong magnet. Degaussers can be rented or purchased. Because of the expense, degaussing is more appropriate for businesses than individuals. It should not be used if someone else will be using the device because degaussing destroys not only the information but also the “firmware” that makes the device run.