The rights of an Internet user acting anonymously conflicts with the rights of a Server victim identifying the malicious user. The ERPINA protocol, introduced in this paper, allows an honest user communicating anonymously with a Server through a PET, while the identity of a dishonest user is revealed. Prior research failed to distinguish objectively between an honest user and an attacker; and a reliable and objective distinguishing technique is lacking. The ERPINA protocol addresses the reliability issue efficiently by defining from the beginning of the communication what is considered as malicious and what is not.