How to restrict download of specified file types in asp.net

In this  post i will show you how to restrict your web app so that .txt
(whatever file extensions you want ) files can not be downloaded/shown.
Open your web.config file and  Register following setting in your web.config

<system.web>
    <httpHandlers> 

<add verb="*" path="*.txt"  

type="System.Web.HttpForbiddenHandler" />
    </httpHandlers>
</system.web>

For more details how to register handler in web.config check
out this link