According to, pseudonymisation of personal data is when certain directly identifying parameters are replaced with pseudonyms (‘codes’) that are unique identifiers. For example, civil registration numbers can be replaced by a code found on a separate list that shows the link between the civil registration number and the code.  

To the greatest possible extent, personal data must be processed in a way which makes it impossible to identify the data subjects, for example under serial numbers rather than civil registration numbers or in an encrypted form.

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