After deleting a user his data will become anonymous. Firstname, surname, city, country and auth method of anonymized users can be set up. Anonymized usernames will be a hash value of old username and deleting time with prefix 'deletedUser_'.  Anonymized e-mail addresses will be the new username with surfix '@delet.ed'.  You can also delay the anonymization by setting up a delay time. Since version 0.4 you can also anonymize users which you have deleted in the past.