What is data anonymization?

Definition

Data anonymization is the process of removing the link between a set of data and the person it describes, so the data can no longer be tied back to that individual.

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Category
Data
Also called
anonymisation, anonymization, data anonymisation
Last updated

NIST defines anonymization as a process that removes the association between the identifying dataset and the data subject. In plain terms: take records about people and strip what points to who they are. What's left can be studied or shared without exposing anyone.

A hospital might publish statistics about patients by age band and region, with names, addresses and record numbers removed. A researcher can see patterns. Nobody can look up a neighbour.

Why it's harder than deleting names

Removing a name is not enough. A postcode, a birth date and a job title can be combined to single someone out. This is easier still when matched against a public record or a people-search profile. Then the data has been re-identified, and it was never really anonymous.

Anonymized vs. pseudonymized

  • Anonymized data can't be linked back to a person at all.
  • Pseudonymized data swaps identifiers for a code, and a separate key can reverse it. It lowers risk but is still personal data under laws such as the GDPR.

Companies sometimes call data anonymous when it is only pseudonymized. If one says it shares your data only in anonymous form, check what is actually removed.

How to protect yourself

  1. 1

    Check what a company means by anonymous

    Look in its privacy policy for whether data is anonymized, or only has your name replaced by an ID.

  2. 2

    Share fewer linkable details

    Birth date, exact postcode and gender together can point to one person. Give a service only what it needs.

  3. 3

    Opt out of data sharing where you can

    Many apps and websites let you turn off sharing or selling of your data in privacy settings.

  4. 4

    Cut down what's linkable about you

    Re-identification needs a second source to match against. Serus finds where your address and phone number are listed publicly and removes them, which leaves less to match.

Serus

See where your personal data is exposed

Serus finds it on data brokers and people-search sites and removes it.

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Frequently asked

Is anonymized data still personal data?

Truly anonymized data, where nobody can be identified, generally falls outside data protection law. Pseudonymized data is still personal data.

Can anonymized data be re-identified?

Yes, if too much identifying detail is left or the data can be matched to another dataset. That is why anonymization has to be done carefully.

What is the difference between anonymization and encryption?

Encryption hides data from people without the key, and the original can be restored with it. Anonymization removes the link to the person for good.

Sources

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