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This page documents the ATTACK_DETECTION_REVERSE_CAPTCHA configuration setting in FormMail.

Type Of Setting


OPTIONAL : you can change this setting if you need to, but the default value is fine for most circumstances.


Implements Reverse CAPTCHA.


ATTACK_DETECTION_REVERSE_CAPTCHA enables the Reverse CAPTCHA attack detection feature for your forms.

Normal CAPTCHA uses image verification to force your users to prove they are human.

Reverse CAPTCHA is a more user-friendly method because it tries to trick a spambot into revealing it is a bot without requiring humans to prove they are human.

To implement Reverse CAPTCHA, you must perform the following tasks:

  1. Create two fields in your HTML form(s):
    • A field that always contains a particular value.
    • A field that always contains no value.
  2. Use CSS or other method to hide these fields from humans.
  3. Set ATTACK_DETECTION_REVERSE_CAPTCHA in FormMail to define these two fields.

You should create random names for the two fields and a random value for the first field. By randomizing your Reverse CAPTCHA, you'll make it different from everyone else's and make it much more difficult for spambots to be created with a single method of attack.

ATTACK_DETECTION_REVERSE_CAPTCHA allows you to use any number of fields to implement Reverse CAPTCHA. However, at least one field must provide a fixed value and at least one field must provide an empty value.

If you don't want FormMail to perform this particular attack detection, set it to an empty array like this:


Default Value



$ATTACK_DETECTION_REVERSE_CAPTCHA = array("cfld1"=>"q7ga","cfld2"=>"");

Where "cfld1" and "cfld2" are your random names for your Reverse CAPTCHA detection fields and "q7ga" is the random content of one of those fields.

See Also