Better Honeypot Implementation (Form Anti-Spam)

How do we get rid of these spambots on our site?

Every site falls victim to spambots at some point. How you handle it can effect your customers, and most solutions can discourage some people from filling out your forms.

That's where the honeypot technique comes in. It allows you to ignore spambots without forcing your users to fill out a captcha or jump through other hoops to fill out your form.

This post is purely to help others implement a honeypot trap on their website forms.

Update:

Since implementing the below honeypot on all of my client's websites, we have successfully blocked 99.5% (thousands of submissions) of all our spam. That is without using the techniques mentioned in the "advanced" section, which will be implemented soon.

Concept

By adding a invisible field to your forms that only spambots can see, you can trick them into revealing that they are spambots and not actual end-users.

HTML

<input type="checkbox" name="contact_me_by_fax_only" value="1" style="display:none !important" tabindex="-1" autocomplete="off">

Here we have a simple checkbox that:

Is hidden with CSS.
Has an obscure but obviously fake name.
Has a default value equivalent 0.
Can't be filled by auto-complete
Can't be navigated to via the Tab key. (See tabindex)

Server-Side

On the server side we want to check to see if the value exists and has a value other than 0, and if so handle it appropriately. This includes logging the attempt and all the submitted fields.

In PHP it might look something like this:

$honeypot = FALSE;
if (!empty($_REQUEST['contact_me_by_fax_only']) && (bool) $_REQUEST['contact_me_by_fax_only'] == TRUE) {
    $honeypot = TRUE;
    log_spambot($_REQUEST);
    # treat as spambot
} else {
    # process as normal
}

Fallback

This is where the log comes in. In the event that somehow one of your users ends up being marked as spam, your log will help you recover any lost information. It will also allow you to study any bots running on you site, should they be modified in the future to circumvent your honeypot.

Reporting

Many services allow you to report known spambot IPs via an API or by uploading a list. (Such as CloudFlare) Please help make the internet a safer place by reporting all the spambots and spam IPs you find.

Advanced

If you really need to crack down on a more advanced spambot, there are some additional things you can do:

Hide honeypot field purely with JS instead of plain CSS
Use realistic form input names that you don't actually use. (such as "phone" or "website")
Include form validation in honeypot algorithm. (most end-user will only get 1 or 2 fields wrong; spambots will typically get most of the fields wrong)
Use a service like CloudFlare that automatically blocks known spam IPs
Have form timeouts, and prevent instant posting. (forms submitted in under 3 seconds of the page loading are typically spam)
Prevent any IP from posting more than once a second.
For more ideas look here: How to create a "Nuclear" honeypot to catch form spammers

We found that a slight (though simple) variation on the suggestions here made a huge difference in the effectiveness of our contact form honeypot. In short, change the hidden field to a text input, and make the bot think it's a password. Something like this:

<input type="text" name="a_password" style="display:none !important" tabindex="-1" autocomplete="off">

You'll note that this mock-password input keeps to the same basic guidelines as the checkbox example. And yes, a text input (as opposed to an actual password input) seems to work just fine.

This apparently minor change resulted in a drastic drop in spam for us.