Countless systems ranging from consumer electronics to military equipment are dependent on integrated circuits (ICs). A surprisingly large number of embedded systems are already security-critical, e.g., medical devices, automotive electronics, SCADA systems or network routers. If the underlying ICs in an applications are maliciously manipulated through hardware Trojans, the security of the entire system can be compromised. In recent years, hardware Trojans have drawn the attention of governments and the scientific community. Even though hardware Trojans have been studied over the last 10 years or so, little is known about how they might look, especially those that are particularly designed to avoid detection. In this talk we introduce several approaches with which a sophisticated attacker could insert Trojan into hardware platforms. We will look at hardware Trojans realized on both, ASICs (application specific integrated circuits) and FPGAs, i.e., programmable hardware.