Protect against a DoS attack without a CAPTCHA

Question

I'd love to know a good way to protect against DoS attacks on my email and contact forms.

I have a "Share with a Friend" function which opens up a form I've created, but I'd rather not put in a CAPTCHA.

I've seen a jQuery + PHP solution here: http://docs.jquery.com/Tutorials:Safer_Contact_Forms_Without_CAPTCHAs#PHP_File

It looks like a good solution, I'd just like some help translating the PHP into C#. I'm guessing an ASHX file would be best to use.

If there are also other (better?) solutions I'd love to hear them.

Answer 1

For the record, a captcha won't help against a DOS attack. The attacking pc's would just be calling your site repeatedly, rendering it unresponsive, without caring about what you return as response (with or without captcha). A capctha will help you against other kind of attacks such as bots and automatic subscriptions.

In case you are using a hosting provider, they should normally protect you form DOS attacks.