I found something very easy that satisfy my needs. Shuffle the order of displaying answers.
I just changed mod/quiz/lib.php line 487 to:
$answerids = explode(",", $options->answers);
//shuffle answers order
srand ((float)microtime()*1000000);
shuffle ($answerids);
foreach ($answerids as $key => $answerid) {
To shuffle the order of questions just add:
shuffle ($questions);
after
$questions = explode(",", $quiz->questions);