Why an extension is added while publishing a site

Question

When i tried to publish a website i see some extension for each and every file that was published why it is happening

<%@ page language="C#" autoeventwireup="true" inherits="Default4, App_Web_oq3urubu" %>

 
You can see the extension

App_Web_oq3urubu

 
Why this is happening for each and every page. What should i d in order to rectify this.