Security · Topic 11 of 13
Data Destruction and Disposal
Compare physical destruction, degaussing, wiping and formatting, and when a certificate of destruction is needed when retiring drives and other media.
- 4 min
- Deleting files or standard formatting does not securely remove data.
- Overwriting or wiping lets a hard drive be reused.
- Use secure erase or cryptographic erase for SSDs.
What it is
Deleting a file or formatting a drive does not reliably remove the data. Before a computer, drive or phone is sold, recycled or thrown away, its data must be made unrecoverable. The method depends on the media type, how sensitive the data is and whether the device will be reused.
How it works
Reuse methods (the device survives)
| Method | What it does | Limits |
|---|---|---|
| Standard (quick) format | Rebuilds the file system and hides the old files | Data can often be recovered with tools |
| Low level format | Rewrites the drive surface and tracks. Often used to mean overwriting the whole drive | Slow on large drives. Modern drives are formatted at the factory |
| Overwriting or wiping | Writes patterns across every sector, one or more times | Works well on hard drives. For SSDs use vendor secure erase tools |
| Secure erase and cryptographic erase | Uses drive built in commands, or destroys the encryption key of an encrypted drive | Suits SSDs and self encrypting drives |
Overwriting with a wiping tool allows the drive to be reused or sold. On a solid state drive (SSD), wear levelling means some blocks are not reachable by normal overwrites, so the drive's own secure erase or cryptographic erase function is the better choice.
Destruction methods (the device does not survive)
| Method | Notes |
|---|---|
| Shredding | An industrial shredder cuts drives and media into small pieces |
| Drilling or hammering | Holes through the platters of a hard drive make it harder to read |
| Degaussing | A strong magnetic field wipes magnetic media such as hard drives and tapes. Does not work on SSDs or optical discs |
| Incineration | Burning the media at a licensed facility |
| Physical pulverizing | Crushing media into dust |
Optical discs and paper are shredded or destroyed in the same spirit. A degausser makes a hard drive unusable, which is why it is a destruction method and not a reuse method.
Outsourcing
A company can hire a third party to collect and destroy media. The provider should issue a certificate of destruction (or recycling) that lists the items and states how they were destroyed.
This certificate is the record needed for audits and compliance. Chain of custody records show who held the media until it was destroyed.
Phones, printers and other devices
Mobile devices should be signed out of their accounts and then reset to factory settings. Because phone storage is normally encrypted, a reset removes the keys and leaves the data unreadable. Office printers and copiers can also keep documents on an internal drive, so wipe or remove that drive before the machine leaves the building.
Company policy and regulations may require a stronger method than a simple reset for sensitive data.
Standards and policy
NIST SP 800-88 (National Institute of Standards and Technology Special Publication 800-88) describes media sanitization. It names three levels: Clear, which uses ordinary methods to remove data from user accessible areas, Purge, which uses stronger methods such as cryptographic erase, and Destroy, which makes the media unusable.
Degaussing counts as a Purge method in the NIST wording, even though it ruins a hard drive. The more sensitive the data, the higher the level.
Choosing a method
If a drive will be sold or donated, choose wiping or secure erase. If it holds highly sensitive data or has failed, choose physical destruction and keep the certificate.
What to remember for the exam
- Deleting files or standard formatting does not securely remove data.
- Overwriting or wiping lets a hard drive be reused.
- Use secure erase or cryptographic erase for SSDs.
- Degaussing works on magnetic media only and makes drives unusable.
- Shredding, drilling, pulverizing and incineration are destruction methods.
- Outsource to a vendor that provides a certificate of destruction.
- NIST SP 800-88 defines Clear, Purge and Destroy.
- Chain of custody tracks media until it is destroyed.
Common mistakes
Trusting quick format. It leaves most of the data on the drive.
Degaussing an SSD. SSDs store data in flash memory, not magnetic platters, so a degausser does not work.
Drilling one hole and calling it done. Drilling reduces risk but a shredder is more thorough for highly sensitive media.
Forgetting the paperwork. Without a certificate or record, there is no proof of destruction.
Check yourself
Which method uses a magnetic field and does not work on SSDs?
Degaussing.
What proves that a vendor destroyed your drives?
A certificate of destruction.
Which erase method suits an SSD that will be reused?
The drive's secure erase or cryptographic erase function.
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