You decide that you want donate your computer to your local charity or a family member. However, you have read the articles about all the data that remains on your hard drive even if you delete the data. How is it that your personal data can be removed from the drive so no one else can see it?
Early in their use of computers, the U.S. Government recognized that hard drives (and now solid state drives) retain lots of data. Some of this data is easily accessible in the “User” area and some less accessible in the systems areas of the hard drive. Prior to replacing the hard drive the data needs to be permanently removed from the hard drive. The process of destroying the data started with a simple writing of any character over all the data area of the drive. The concept of what we now call “wiping” has developed into a standard employed across the U.S. Government and adopted worldwide a sbest practices for wiping hard drives. The standard developed as U.S Department of Defense standard DoD 5220.22-M. It outlined the recommend methodology for destroying data using software methodology. The standard listed suggestions from a single pass of the data area with random characters to 30 passes over the data. This methodology has changed and most in the field recognize that based on the current hard disk drives configuration a single pass sufficiently destroys all the data for non-classified storage devices. Classified storage devices are physically destroyed. All of the recommended methods of data wiping are just that, recommendations. The agency retaining the data has to decide the method and procedure required to destroy the data based on the data’s significance.
The National Institute of Science and Technology (NIST) released in December of 2014 an updated version of its Guidelines for Media Sanitization. Some of the recommended factors to be considered are included from page 11:
“Organizations should consider environmental factors including (but not limited to):
- What types (e.g., optical non-rewritable, magnetic) and size (e.g., megabyte, gigabyte,and terabyte) of media storage does the organization require to be sanitized?
- What is the confidentiality requirement for the data stored on the media?
- Will the media be processed in a controlled area?
- Should the sanitization process be conducted within the organization or outsourced?
- What is the anticipated volume of media to be sanitized by type of media?
- What is the availability of sanitization equipment and tools?
- What is the level of training of personnel with sanitization equipment/tools?
- How long will sanitization take?
- What is the cost of sanitization when considering tools, training, verification, and reentering media into the supply stream?”
These are all good things to consider in a small business and may still be relevant in our personal decision making process. The NIST guide describes types of data deletion as Clearing, Purging or Destruction. Clearing and Purging relate to the actual overwriting of the data on the drive and Destruction is the physical destruction of the hard disk drive.
For the average computer user the most likely question becomes what is the intended use of the hard drive after the data destruction. Its generally that you want it to work after the data is removed or you don’t. If you want it to work, a data wiping program is the most useful tool or technique. In this case the data is destroyed and the hard disk drive can be reused. Physical destruction is just that, the data drive is no longer accessible due to the physical destruction of the hard disk drive. The government’s consideration of destruction is usually the use of a large shredder or destruction device capable of dealing with hard drives. However, most physical destruction to the drive (hammering in until its flat) will make the data unrecoverable for the average persons intentions.
Another old school method of destruction is the use of a Degausser (commonly used in destroying data on tape). Degaussing as defined by NIST is:
“To reduce the magnetic flux to virtual zero by applying a reverse
magnetizing field. Degaussing any current generation hard disk
(including but not limited to IDE, EIDE, ATA, SCSI and Jaz) will
render the drive permanently unusable since these drives store track
location information on the hard drive.”
The magnetism required has to be sufficient enough to change the magnetic field on the drives platters. Smaller older Degaussers can render the drive inoperable but may fail to destroy the data on the drives platters. The NSA has an approved list of degaussing tools that can be found in their Deagausser Evaluated Products List.
Something you may want to consider also is getting a certification of the data destruction. Once the data is destroyed verifying the destruction is a normal part of the process. Using data wiping tools the person or company verifying the data destruction can look at the data storage space and see that the data was destroyed. Using physical methods such as shredding, the drive owner can see that the drive is physically destroyed. Degaussing as a method is the only one that has a difficult level of determining the data’s destruction. Providers of data destruction services can provide letters or documents of the destruction.
Whether it is a personal decision or for implementation in a small business your decisions about data wiping are:
1) What is the intended use of the hard drive after the data is destroyed?,
2) What method of destruction should I use?, and
3) What will the cost be for destroying the data?
4) Do I need certification of the data’s destruction.
Any full service data recovery company can assist you with your decision making and will offer one or all of the types of destruction processes mentioned and should offer a certification of the destruction.