I set up a form on a customer website two days ago and it is already getting spammed. Is there any chance you can add in a security image or some form of check before a form is submitted?
If it is a form you created "by hand" , have a look at the "recaptcha" module and add it to the form. There is no "standard" solution for protecting a user-defined-form from spambots.
There is a discussion about it @ the dev-forums , I didn't succeed (yet) in implementing the recaptcha on user-defined-forms.