This work seeks to expose the vulnerability of un-trusted computing platforms used in critical systems to hardware Trojans and combined hardware/software attacks. As part of our entry in the Cyber Security Awareness Week (CSAW) Embedded System Challenge hosted by NYU-Poly in 2011, we developed and presented 10 such processor-level hardware Trojans. These are split in five categories with various impacts, such as altering instruction memory, modifying the communication channel, stealing user information, changing interrupt handler location and RC-5 encryption algorithm checking of a medium complexity micro-processor (8051). Our work serves as a good starting point for researchers to develop Trojan detection and prevention methodologies on modern processor and to ensure trustworthiness of computing platforms.