Data Destruction

When removing software, we need to be very careful not to cause a breach of data privacy or integrity.

Data Retention Policies

Data retention can be based on legal requirements or business needs. Other case can be because of fear of liability or cost of retention.


Data retention is the ability to recover old data, for example for regulatory inquiries.

This means we need to think about the lifespan of media: is that a media type we will still be able to use in 20, 40 years? The media were the data is stored also have deterioration point.

End of Live Data

End of life data can be archived to prevent cluttering of database.

The question is “is the data encrypted?” and if yes, we must keep the encryption tools and the algorithms available as well for recovery.

Note: this also applies to backups.

When we want data to be deleted, we need to be very careful about recovery. This is specially true when dealing with privacy.


Once again, we need procedures:

Data disposal can be done in several ways:

  • Deletion
  • Overwrite
  • Purge
  • Degaussing (magnetic force to reduce the magnetic flux density back to 0 making it difficult to recover the data)
  • Crypto shredding/erasure (delete the encryption key to prevent recovering of encrypted data)
  • Destruction (physically chew it up and/or melt it down)

Residual Data

Data remanence is something to fear: data that were not correctly deleted and are still recoverable somehow.

For some types of media such as HDD, SSD, tapes and optical disks, physical destruction is the most secure way to make sure there is no residual data left for someone to snoop in.


There are things we want to keep: for example for historical significance (memorabilia).

When doing so, we need to be careful of:

  • Age of media: will the media be unusable at some point?_
  • Ability to read all media: will we still be able to read the media?
  • Encryption keys: to be able to decrypt the data

Key points review: Ensure data is retained or disposed of according to policy. Secure (defensible) data deletion: we have assurance the data was deleted.