Question

On this site if you do too many clicks or post comments too fast or something like that you get redirected to the “are you a human” screen. Does anybody know how to do something similar?

Answer 1

Here is a very nice Captcha Control for asp.net that first of all you need

http://www.codeproject.com/KB/custom-controls/CaptchaControl.aspx

Then you can use it together with this idea that try to find the dos attacks

http://weblogs.asp.net/omarzabir/archive/2007/10/16/prevent-denial-of-service-dos-attacks-in-your-web-application.aspx

be ware of a bug in this code in line if( context.Request.Browser.Crawler ) return false;, its must return true, or totally remove it for sure.

and make it your compination for the clicks, or submits.

If a user make too many clicks on a period of time, or many submits, then you simple open the capthaControl, and if the clicks are by far too many, then triger the dos attact. This way you have 2 solution in one, Dos attact prevent, with captcha at the same time.

I have made somthing similar my self, but I have change the source code of both, a lot to feet my needs.

One more interesting link for a different code for the dos attack.

http://madskristensen.net/post/Block-DoS-attacks-easily-in-ASPNET.aspx

Hope this help you.