This paper addresses the Hardware Trojan issues in passive EPC C1G2 RFID Tags. We propose in this paper to study the insertion of malicious circuit in EPC GEN2 RFID tags. The description and the implementation of several different Hardware Trojans are first discussed. Then they are all evaluated in an EPC GEN2 environment using a dedicated FPGA based tag emulator. The evaluation focuses on criteria such as Trojan detection, design cost and EPC gen2 compliance.