原版Block-Spam-By-Math只是用rand函数随机产生了了2个整数(mathvalue0、mathvalue1)算加法(mathvalue2)
rand函数参考：http://www.w3school.com.cn/php/func_math_rand.asp

......
function add_hidden_fields()
{
	$mathvalue0 = rand(2, 15);
	$mathvalue1 = rand(2, 15);
	echo '<div>';
	echo "What is $mathvalue0 + $mathvalue1 ?";
	echo '<input name="mathvalue2" type="text" />';
	echo '<strong>IMPORTANT!</strong> To be able to proceed, you need to solve the following simple math (so we know that you are a human) :-)</div>';
	echo '<div style="display: none;">Please leave these two fields as-is: ';
	echo "<input name="mathvalue0" type="text" value="$mathvalue0" />";
	echo "<input name="mathvalue1" type="text" value="$mathvalue1" />";
	echo '</div>';
}
......
// Check for hidden fields and wp_die() in case of error
function check_hidden_fields()
{
	// Get values from POST data
	$val0 = '';
	$val1 = '';
	$val2 = '';
	if ( isset( $_POST['mathvalue0'] ) ) {
		$val0 = $_POST['mathvalue0'];
	}
	if ( isset( $_POST['mathvalue1'] ) ) {
		$val1 = $_POST['mathvalue1'];
	}
	if ( isset( $_POST['mathvalue2'] ) ) {
		$val2 = $_POST['mathvalue2'];
	}
	// Check values
	if ( ( $val0 == '' ) || ( $val1 == '' ) || ( intval($val2) != (intval($val0) + intval($val1)) ) ) {
		// Die and return error 403 Forbidden
		wp_die( 'Bye Bye, SPAMBOT!', '403 Forbidden', array( 'response' => 403 ) );
	}
}
......

如何改造复杂一点呢？

直接增加计算复杂程度就好了：加减乘除，甚至你可以平方立方，平方根立方根

我所用的方法：2个随机整数A、B先放大N倍算加法再缩小N倍然后减一个随机数C

即 (A*N + B*N)/N – C

N完全是一个无需在input中体现出来的数字，但是复杂程度已经大大增加了，如果你想继续复杂你可以继续放大再缩小 加了再减。。随便你

目前效果： 已经100%杜绝SPAM

......
function add_hidden_fields()
{
	$mathvalue0 = rand(1, 11);
	$mathvalue1 = rand(1, 21);
	$mathvalue2 = rand(1, 31); $mathvalue2=$mathvalue2*3;
	$mathvalue3 = rand(1, 41); $mathvalue3=$mathvalue3*4;
	echo '<div style="border: 1px solid #EEE; border-left: 10px solid #EEE; border-right: 10px solid #EEE; line-height: 25px; padding: 5px; margin: 0px;">';
	echo "<span style="color: red;"><strong>Required: (".($mathvalue0*$mathvalue2)."+".($mathvalue1*$mathvalue2).")/$mathvalue2-".$mathvalue3."=</strong></span>";
	echo '<input name="mathvalue2" size="3" type="text" />';
	echo '</div>';
	echo '<div style="display: none;">Please leave these two fields as-is: ';
	echo "<input name="mathvalue0" type="text" value="$mathvalue0" />";
	echo "<input name="mathvalue1" type="text" value="$mathvalue1" />";
	echo "<input name="mathvalue3" type="text" value="$mathvalue3" />";
	echo '</div>';
}
......
// Check for hidden fields and wp_die() in case of error
function check_hidden_fields()
{
	// Get values from POST data
	$val0 = '';
	$val1 = '';
	$val2 = '';
	if ( isset( $_POST['mathvalue0'] ) ) {
		$val0 = $_POST['mathvalue0'];
	}
	if ( isset( $_POST['mathvalue1'] ) ) {
		$val1 = $_POST['mathvalue1'];
	}
	if ( isset( $_POST['mathvalue2'] ) ) {
		$val2 = $_POST['mathvalue2'];
	}
	if ( isset( $_POST['mathvalue3'] ) ) {
		$val3 = $_POST['mathvalue3'];
	}
	// Check values
	if ( ( $val0 == '' ) || ( $val1 == '' ) || ( $val3 == '' ) || ( intval($val2) != (intval($val0)+intval($val1)-intval($val3)) ) ) {
	// Die and return error 403 Forbidden
		wp_die( 'Bye Bye, SPAMBOT!', '403 Forbidden', array( 'response' => 403 ) );
	}
}
......