Malicious alterations of integrated circuits (ICs) and systems, introduced during either the design or the fabrication process, are increasingly perceived as a serious concern by the semiconductor industry. Such rogue alterations often take the form of a hardware trojan, which may be activated from remote after the compromised chip or system has been deployed in the field. The devious actions of hardware trojans can range from the disabling of all or part of the chip ("kill switch"), through the activation of a backdoor that allows an adversary to gain access to the system, to the covert transmission of sensitive information (e.g. cryptographic keys) off-chip. In the recent past, hardware trojans which induce side-channel leakage to convey secret keys have received considerable attention. With the present paper we aim to broaden the scope of trojan side-channels from dedicated cryptographic hardware to general-purpose processors on which cryptographic software is executed. In particular, we describe a number of simple micro-architectural modifications for inducing or amplifying information leakage through faulty computations or variations in the latency (and power consumption) of certain instructions. We also propose novel software-based mechanisms for trojan activation and present two case studies to exemplify the induced side-channel leakage for software implementations of RSA and AES. Finally, we discuss a constructive use of micro-architectural trojans for digital watermarking so as to facilitate the detection of illegally manufactured copies of processors.