A processor system comprising: performing a compilation process on a computer program; encoding an instruction with a selected encoding; encoding the security mutation information in an instruction set architecture of a processor; and executing a compiled computer program in the processor using an added mutation instruction, wherein executing comprises executing a mutation instruction to enable decoding another instruction. A processor system with a random instruction encoding and randomized execution, providing effective defense against offline and runtime security attacks including software and hardware reverse engineering, invasive microprobing, fault injection, and high-order differential and electromagnetic power analysis.