Simple spam protection on contact forms using hidden input field

If we have contact forms in website, the spam mails will be the most annoying things in our inbox.

But using a simple hidden input fields, we can escape from almost spam bots.

Now we are going to make a contact form with a hidden input field. We like to hide this input field using CSS. So a normal user never seen this input field and even if the CSS fails to load, they get a note explaining what to do.

But in general, bots struggle with reading CSS or JavaScript. So when a spam bot looks at this, it sees a good spot to stick whatever spammy url they’re trying to advertise.

In server-side, before doing any actions on this contact form, we will check the value of that hidden input field. If there is a value, that means this contact request was submitted by a spam bots and we will throw it out.

The HTML

<form action="/submit.php" method="post">
	<p>Your name: <input type="text" name="name" /></p>
	<p>Your email: <input type="text" name="email" /></p>
	<p style="display:none;">Leave this empty: <input type="text" name="url" /></p>
	<p><textarea name="message"></textarea></p>
	<p><input type="submit" value="Send" /></p>
</form>

The PHP

<?php
// if the url field is empty 
if(isset($_POST['url']) && $_POST['url'] == ''){
	 // then send the form to your email

} else {
	// Do some actions for spam bot
}
?>

Now the PHP script on the server can tell who is a spammer and who isn’t. The regular people can sent contact request & the spammers get ignored! That is enough.

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This article was published on February 27, 2015

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