1. A method of anonymizing personalized event data, comprising the steps of: receiving the personalized event data further comprising event data and an encrypted personal identifier; determining, whether an entry exists for the encrypted personal identifier in a key database of the data system in which the encrypted personal identifier is associated with a system identifier that uniquely identifies the encrypted personal identifier in the data system and where the encrypted personal identifier is uniquely associated to the one system identifier; determining where if no entry is detected in the key database for the received encrypted personal identifier then: generating a new entry for the key database in which the received encrypted personal identifier is uniquely associated to a new system identifier; storing the received encrypted personal identifier associated to the new system identifier as the new entry in the key database; storing the new system identifier associated to the event data contained in the personalized event data in an event database and storing the system identifiers in association with the corresponding event data; determining whether an entry exists for the encrypted personal identifier in the key database is carried out on a basis of a ciphertext of the encrypted personal identifier; encrypting the ciphertext of received encrypted personal identifier by the data system using asymmetric encryption before it is determined whether an entry exists in the key database for the encrypted personal identifier and where the encrypted personal identifiers contained in the entries of the key database were encrypted by the data system using the same asymmetric encryption before storing; and automatically deleting a key used for asymmetric encryption of the ciphertext when a request for a data output other than the new system identifier or event data is detected.