(This blog post was created in year 2010. You can now include Google reCAPTCHA in web-to-lead/web-to-case forms to prevent the spamming. Please refer to my new blog post Step By Step Guide to Setting Up Web-to-Lead & Web-to-Case in Salesforce with reCAPTCHA on how to prevent the spam – updated on 25-Feb-2020)

If you are using web-to-lead form to capture leads from your website directly into Salesforce, there is a very high chance of getting hundreds and thousands of junk or spam leads. If you want Salesforce to do something about it please vote for the idea at URL http://sites.force.com/answers/ideaView?id=08730000000BrZkAAKAnd while we are waiting for Salesforce to come up with the solution, here is what you can do.More