Module 2 · Anonymous vs pseudonymous data
Anonymous data is rendered unidentifiable and is NOT protected by the GDPR, but true anonymisation is hard. Pseudonymous data is NOT fully anonymous - identifying aspects are detached but the data can be re-identified with separately held information, so it remains personal data subject to the GDPR. Pseudonymisation is a security measure that reduces risk and is a factor in assessing risk for breaches and transfers.
| Anonymous data | Pseudonymous data | |
|---|---|---|
| Re-identifiable? | No - cannot be traced back | Yes - with additional information kept separately |
| GDPR applies? | NOT protected by the GDPR | Remains personal data subject to the GDPR |
| Nature | Rendered unidentifiable | A security measure that reduces risk |
| Examples | Aggregated statistics with no identifiers; de-identified health data | "Customer A" coded data; encrypted records with the key stored separately; tokenised card numbers |
Pseudonymous data can be re-identified with additional information and so stays under the GDPR; properly anonymous data cannot be traced back and falls outside the GDPR. True anonymisation is hard - data can become identifiable by a small margin.
The fact that data is pseudonymous is a factor in assessing risk (e.g. for breach notification or international transfers). Masking / data obfuscation manipulates real data to reduce risk while preserving desired properties.