Step 1 – go to http://www.google.com/recaptcha/intro/index.html and sign up. You'll need the keys here for later.

Step 2 – In folder /application/controllers/ open 'main.php'. On line 18, replace #################################### with your SECRET key from step 1. 

Step 3 – In folder /application/views/_base_override/main/pages open 'main_contact.php'. On line 41, replace #################################### with your PUBLIC key from step 1. Uncomment this line by removing '<!--' and '-->' at each end.

Step 4 – In the same folder, open 'main_join_2.php'. At line 130, replace #################################### with your PUBLIC key from step 1. Uncomment this line by removing '<!--' and '-->' at each end.

Step 5 – Enjoy no longer receiving spam on your contacts and join pages!