In this tutorial, I will show how to add CAPTCHA module to the Drupal 7 webform. Why? I was sick and tired to manually block spammer's IP addresses.
In order to work with this tutorial, you will have to install CAPTCHA and Webform modules.
I will assume, you have already configured your webform, now lets add captcha to it, and keep those spammers away from our precious websites.
There is great documentation already on Drupal site, you can follow it here: Adding CAPTCHA to a Webform
Go to admin/config/people/captcha/captcha/settings in the blank text box under "Form Protection" enter the form_id (not the node id) of the webform and save the configuration. Go to the webform page (as Anonymous user) and you should be able to see the captcha there.
To quickly find the form_id of the webform, take the node id and append it to "webform_client_form_", for example if the node id is 3 your webform form_id will be "webform_client_form_3". You can also use firebug to inspect the form_id field.
That's it. Now you are safe. Or at least a bit safer!