A method for detecting a fault injection is described. The method includes providing a secondary code, the secondary code including a predetermined function with a known expected result when the secondary code is executed with a known tested input. A primary code is executed in the data processing system. The primary code may be a portion of code that requires protection from a fault injection attack, such as for example, security sensitive code. The secondary code is executed in parallel with the primary code execution in the data processing system to produce an output. The output is compared with the known expected result to detect the fault injection attack of the data processing system. In one embodiment, the secondary code is not related to the primary code.