Hidden form field to prevent spam

Most of the website has a contact form to send emails to webmasters. And most of these forms are targeted by spam bots. They automatically fill the data’s in the form elements and submit these data’s and as a result our mail box will full of spam emails.

In order to avoid this spam emails we can use Captcha . A Captcha is an image that contains a verification code. It may be a text or a number, or a combination of both
The user must enter the verification code to prove that the entry is not a spam. We are checking the verification code in the server side. But now a day’s spam bots have the ability of character recognition and probably they can break the Captcha. So we need to increase the complexity of Captcha verification code. But it will very difficult for users to read the verification code.

Hidden Form Field

This is one simple way to prevent the spam data’s. This is also knows as Invisible Captcha. Just add an extra hidden field in the form. Using css hide the visibility of the text box. Noramlly humans can't see the hidden form elements and they wont fill the datas. So the this field remains empty.But spam bots are fill all form elements. So in the server side we can check the hidden filed value , and can check whether it’s a spam or not.

Example :

<label for="email">Email:</label><input type="text" name="txtemail" value="" />
<input class="confirmation-field" type="text" name="txtCaptcha" value="" />
<style>
.confirmation-field { display: none; }
</style>