RFID (Radio Frequency Identification) tags use lightweighted security methods because of cost constraints. In this paper a lightweight security method is investigated and proved that it significantly lacks in protecting RFID tags against simple cloning attack. In order to protect RFID tag from cloning attacks a novel security method is proposed in this paper. The proposed security method provides high level computational difficulty against the three basic attacking techniques, i.e. eavesdropping, replay and man in the middle. In order to clone a tag, attacker eavesdrops the tag responses and creates a replica of the tag. The novel security method presented in this paper increases the hardness to avoid guessing tag secrets resulting in a conditional none clone able tags. The proposed security method is also evaluated using propositional logic proofs to demonstrate the level of security it can provide.