Hidden Form Fields To Prevent Bot Spam

Augie (a creative real estate investor) presented a spam prevention method idea which we’ve been talking about under a previous post this past week: HowTo Eliminate Wordpress Trackback Comment And Pingback Spam. The basic idea is to provide an extra input field which is hidden to a user when viewed normally from the browser. This means if you check your form data when a submission is being processed, you can determine if the field is still empty. If it is filled out, then a bot must have auto filled the field.

Spam Field Details

The naming convention used on a hidden field should be named “email” or “url” to trick the bot. Your real email field will then of course need to be named something else. A small price to pay for less house cleaning.

Another key to all of this is to wrap your trap (haha) in a DIV so that the a bot cant tell that the field is hidden. Marking it with type=”hidden” on the input tag itself is a bit of a giveaway. Assigning an id or class to the div and specifying display:none; would cause the bot a lot of extra work which most probably aren’t programmed for. You could also use a built in id or class directly on the div to specify it as a hidden field.

Hidden Input Field Code

Here is an example of what your code would look like:

1. CSS code would look like this:
2. #email {
3. display: none
4. }
5.  
6. OR if you're doing it by the div:
7.  
8. .specialfield {
9. display: none
10. }
11.  
12. Your form would look something like this:
13. <form method="post" action="yourformprocessor.php">
14. <div class="specialfield"><input id="email" type="text"></div>
15. <input id="realemail" type="text">
16. </form>
17. Download this code: 1113spamformcode.txt

Using Hidden Fields

It isn’t too much of a stretch to add this to a custom solution or implement it into a Wordpress comments or form plugins because id’s and classes are assigned to input fields by default. If you’re not already using a form plugin check out:

cforms II or Contact Form 7 (my preference).

If I get enough requests I’ll write a post which explains how to implement this into Wordpress comments in a similar manner in which I setup the Enhanced Numbered Equation CAPTCHA.

The More Spam Defense The Better

I don’t have a lot of experience in using spam bots, but this is a promising way to enhance our line of defense against spam. More importantly, its not intrusive on a users browsing experience. Unlike a CPATCHA, it requires a valid visitor to do nothing!

If you have any thoughts or comments, about this spam technique, leave them below.

Posted by: Rob
Category: Coding
Tags: PHP, Plugins, Spam, Wordpress
Respond: Leave A Comment | Trackback URL