ASP。有没有一种方法可以忽略一个请求?

I have an ASP MVC3 website with a rest API service. When a user passes in an invalid API or they have been blacklisted i wish to ignore the response. I know I could send back a 404 or pass back an 503 but if someone keeps polling me then I would ideally like to ignore the response causing a time-out their end. Thus delaying the hammering my server gets.I have an ASP MVC3 website with a rest API serv