1. A method for constructing a control flow graph (CFG) from a computer executable program the instructions of which belong to one or more instruction sets, said method comprising the steps of defining a number of block leader types including at least one type related to an instruction set change, block leaders specifying basic block boundaries in the program, said basic blocks including instructions or data ( 702 ), building a CFG structure comprising basic blocks found in the program ( 708 ), adding control flow and addressing information to said CFG by propagating through said basic blocks and internals thereof ( 710 ).