Add spam protection to my form? 1+2=3 ?

I have form on my companies website that isn't being attacked my spammers.

I am looking for a simple piece of code to put in the form above the submit button. Something simple like "1+2= ..." then they have to put in 3, or the form rejects. If the put in the correct answer, then the form submits.

How can I do this?

 

Depends....

1) are you wanting the "test" to be static or dynamic (ie is it always 1 + 2 or is it RandomNumber1 RandomMathsFunction RandomNumber2 = ...?)

2) What serverside language are you using? PHP? .Net?

 

we're using php ..

And the test can be static.

 

It's usually done by generating 2 random numbers (usually between 1 and 20) and then adding them together. Then, storing a hash of the answer in a session. When the form is submitted, check the form input (hashed) against the session variable.

 

$questions[] = array('question','answer');
$questions[] = array('question','answer');
$questions[] = array('question','answer');

//form start
$x = rand(0,count($questions)-1);
echo $questions[$x][0];
echo '<input type="text" id="ans" name="ans"  value="">';
echo '<input type="hidden" id="q" name="q" value="$x">';
//form end

//In your submit validation

$pos = $_POST['q'];
if($_POST['ans'] != $questions[$pos][1]){ die('Invalid answer');}

PHP:

Peace,