1. A method for disguising an operation contained in a software program, said operation having at least one variable, the method comprising: a) identifying said operation to be disguised in said program; b) assigning a predetermined bias constant and a predetermined scaling constant to the or each of said at least one variable; c) determining an equivalent expression logically equivalent to said operation, said equivalent expression having at least two expression constants, each of said at least two expression constants being based on at least one factor selected from a group comprising: a scaling constant (s) for one of said at least one variable; a bias constant (b) for one of said at least one variable; an additive inverse modulo n (b −1 ) of said bias constant where said additive inverse modulo n is the value for b −1 where (b+b −1 ) (mod n)≡0; a multiplicative inverse modulo n (s −1 ) of said scaling constant where said multiplicative inverse modulo n is the value for s −1 where (s*s −1 ) (mod n)≡1, d) replacing said operation with said equivalent expression in said software program.