Each method can return3507 # three status:3508 # * the system is known to be safe (returns '1');3509 # * the system is known to be unsafe (returns a string that identifies3510 # the system, e.g. 'IBM');3511 # * the method does not permit to detect wether the system is safe3512 # (returns 0).3513 # We then combine both results to come to a conclusion.