As I started getting too many spams because of bots, I implemented Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA) in all the interactive pages of my site.
Took the control from here http://www.codeproject.com/KB/custom-controls/CaptchaControl.aspx, and customized according to my needs. The code was easy to understand and customize.
Disclaimer The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.