Methods and apparatuses for obfuscating computer instruction streams. In one aspect of the invention, an exemplary method includes breaking each of at least two operative instruction streams into a plurality of parts and interleaving the parts into a new instruction stream. In another aspect of the invention, an exemplary method includes breaking each of at least two operative instruction streams into a plurality of parts and interleaving the parts with obfuscation codes into a new instruction stream. The obfuscation codes interrelate the parts from different instruction streams to prevent reversal of interleaving.