Easiest way to block spam

ThomasP · #1 13-04-2007, 19:30

Our guestbook has been attacked by spam bots quite a bit recently and I finally got around to stopping the spam with a neat little trick from the ASP.NET AJAX Control Toolkit that real users won't even notice (as long as they have Javascript enabled...)

PHP Code:


			
<?PHP

    if($_POST['Bot'] == "Yes")

        echo 'You're a bot! Stop messing with my form!'

    else if($_POST['Bot'] == "No")

        echo 'Hi ' . $_POST['name'] . '!'

?>

<form action="test.php" method="POST">

Name: <input type="text" name="name">

<input type="hidden" id="Bot" name="Bot" value="Yes">

<script type="text/javascript" language="javascript">

document.getElementById('Bot').value = "No"

</script>

<input type="submit">

</form>

A lot of spam bots don't execute javascript so you are safe from them. For people that disable javascript, you can modify the above code to do something like...

PHP Code:


			
<form action="test.php" method="POST">

<?PHP

    if($_POST['Bot'] == "Yes") {

?>

I'm not sure if you're a bot or not... what is five plus eight?<br />

<input type="text" name="HumanTest">

<input type="hidden" name="name" value="<? echo $_POST['name'] ?>">

<input type="submit">

<?

    } else if($_POST['Bot'] == "No" || $_POST['HumanTest'] == "13" || $_POST['HumanTest'] = "thirteen") {

        echo 'Hi ' . $_POST['name'] . '!'

    } else {

?>

Name: <input type="text" name="name">

<input type="hidden" id="Bot" name="Bot" value="Yes">

<script type="text/javascript" language="javascript">

document.getElementById('Bot').value = "No"

</script>

<input type="submit">

<? } ?>

</form>

And that will allow regular people that have javascript enabled to not be bothered by proving they're human while also allowing for the occasional user that disables it.

Disclaimer: It has been a while since I've wrote any PHP so I can't guarantee any of that PHP code will work.

artdutra04 · #2 13-04-2007, 22:31

Quote:

Originally Posted by ThomasP

Disclaimer: It has been a while since I've wrote any PHP so I can't guarantee any of that PHP code will work.

The code looks good so far, but I found an error in the second block of code. The changes I made are added in red:

Code:

...
<input type="submit">
<?
    } else if($_POST['Bot'] == "No" || $_POST['HumanTest'] == "13" || strtolower($_POST['HumanTest'] == "thirteen")) {
        echo 'Hi ' . $_POST['name'] . '!'
    } else {
?>
Name: <input type="text" name="name">
...

This change fixes the single equals sign operator error, as well as added in a strtolower() command, so that if the user inputs Thirteen or tHirTeeN you know they still had the right answer.

ThomasP · #3 14-04-2007, 03:22

Quote:

Originally Posted by artdutra04

The code looks good so far, but I found an error in the second block of code. The changes I made are added in red:

Code:

...
<input type="submit">
<?
    } else if($_POST['Bot'] == "No" || $_POST['HumanTest'] == "13" || strtolower($_POST['HumanTest'] == "thirteen")) {
        echo 'Hi ' . $_POST['name'] . '!'
    } else {
?>
Name: <input type="text" name="name">
...

This change fixes the single equals sign operator error, as well as added in a strtolower() command, so that if the user inputs Thirteen or tHirTeeN you know they still had the right answer.

Thanks artdutra, I've been doing too much with VB.NET and SQL at work lately, I kept starting to type "OR" instead of "||" also but managed to catch all of those mistakes.

I was thinking about the spam blocking code a minute ago and think there may actually be a better way to do the thing...

PHP Code:


			
<html>

<body>

<?PHP

    if((strtolower($_POST['Bot']) != "thirteen" && $_POST['Bot'] != "13"))

        echo "You're a bot! Stop messing with my form!";

    else

        echo 'Hi ' . $_POST['name'] . '!';

?>

<form action="test.php" method="POST">

Name: <input type="text" name="name">

<script type="text/javascript" language="javascript">

document.write('<input type="hidden" id="Bot" name="Bot" value="Yes">');

document.getElementById('Bot').value = "13";

</script>

<noscript>

  What is eight plus five? <input type="text" id="Bot" name="Bot" />

</noscript>

<input type="submit">

</form>

</body>

</html>

I also caught another error when I actually tested that before posting... I had used apostrophes in my PHP strings and had one in "You're", switched that string to quotation marks.

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