1. A non-transitory computer readable medium having computer executable instructions for implementing a method of deterministic reply of a computer program, the method comprising: identifying in machine code representing said program, instances of machine code instructions for a first process that accesses a portion of shared memory; identifying a second process that accesses said shared portion of memory; wherein both said first and second processes have read and write permissions to access said shared portion of memory; modifying said program machine code such that one of processes has read and write permission to access said shared portion of memory and the other said process has only read permission to access said shared portion of memory; identifying when said other process attempts to write to said shared portion of memory; and executing an instruction sequence in response to said identifying of said attempted write.