ASP.NET blog by Subgurim

AntiSpam HttpModule

I hate the Spam robots, and they hate me. I also hate captchas... so, how can I avoid that they write garbage on my websites?

This HttpModule, with three (1+2) basic rules (the last is optional) has been the solution:

using System;
using System.Web;

namespace Subgurim.Tools
{
    public class AntiSpamModule : IHttpModule
    {
        public void Init(HttpApplication app)
        {
            app.BeginRequest += new EventHandler(AntiSpamFilter);
        }

        private void AntiSpamFilter(object sender, EventArgs e)
        {
            HttpResponse response = ((HttpApplication)sender).Response;
            HttpRequest request = ((HttpApplication)sender).Request;

            // 1.- They are sending a  POST
            // 2.- The call doesn't provide from any other page
            // 3.- The call provides from another page but it's not on my domain.
            if ((request.Form.Count > 0) &&
                    ((request.UrlReferrer == null) ||
                    (!request.UrlReferrer.Authority.Equals(request.Url.Authority, StringComparison.InvariantCultureIgnoreCase))))
            {
                try
                {
                    response.End();
                }
                catch (System.Threading.ThreadAbortException ex)
                {
                    // No hacer nada
                }
            }
        }

        public void Dispose()
        {
        }
    }
}

Configure the HttpModule inside the system.web of your web.config and that's all.

    <system.web>
        <httpModules>
            <add name="AntiSpamModule" type="Subgurim.Tools.AntiSpamModule"/>
        </httpModules>
    </system.web>