Hi,
We just uploaded a new contribution/add-on that you might want to consider. You can find the Form Armor Module for Zen Cart at:
http://www.zen-cart.com/index.php?main_page=product_contrib_info&cPath=40_47&products_id=1202
Form Armor is a hosted subscription service that protects Web site forms against spam and abuse without requiring CAPTCHA images, math puzzles or other user tests. (Basically, we help your Web site forms look like regular forms again, but without the spam hassles.)
Thanks to DrByte and the rest of the Zen Cart Team, the module makes it super easy to use the Form Armor service with the Contact Us form and Tell-a-Friend form in your ZC shop.
If you'd like to give it a try, you can learn more and set up an account at https://www.formarmor.com/zencart/. There is a $9/month subscription fee for the service, and a portion of your monthly fee goes straight back to support the Zen Cart project. We also have a 100% satisfaction guarantee, so if you try it and then decide it's not right for you, just let us know in the first 30 days and we'll refund your subscription.
I'll also add that I agree with christon26, that locking out IP addresses can be really hit or miss and you can easily and accidentally lock out potential customers, too. :yuck:
If you have questions let me know and I'll be glad to help where I can. Thanks!
Larissa Reynolds, Co-founder
Form Armor
http://www.formarmor.com/zencart/