Abstract: A method for detecting a fault condition in a computer processor operating a main control program, comprising the steps of sequentially performing a plurality of functions on an initial input value so as to compute a final value, the input value to each of the second and subsequent functions being provided by the output value from the preceding function in the sequence; loading at least one self-test module onto the computer processor for detecting whether a fault condition has occurred in the computer processor, wherein at least one of the functions is carried out within a self-test module; and comparing the computed final value with a predetermined value to provide an indication of whether a fault condition has occurred in the computer processor. The invention also relates to an apparatus for detecting a fault condition in a computer processor.