This module provides a simple solution to limit automated spam webform submissions for Drupal 7. Compared to captcha solutions, it won't penalize real visitors with characters often too much difficult to read.
Download the module to your module folder and enable it. That's it.
Dependency : webform.module
The module automatically adds 2 non-visible fields to any webform on your Drupal web site. These fields are not stored in the database and thus don't impact the submissions content. This anti-spam approach is simple yet sufficient to prevent most automated spam robots to spam Drupal webform: when user fills out the webform, these fields must stay empty otherwise the webform won't validate.