Abstract—Hardware security is considered a major design and manufacturing target area with a broad range of research and development topics such as protection of intellectual property (IP), metering of hardware, detection of hardware Trojans, and a lot of other topics. This paper discusses Trojan realization in integrated circuits (ICs), as well as the possible security measures, also exploring the usage of the 3-D integration in hardware security where additional hardware can be mounted after fabrication to foster secure execution just for those systems which need it.