Howto block unwanted requests to your apache server with DD-WRT

Recently I made a mistake while configuring my Apache web server and the whole world found out that I have an open proxy (which I don't... at least not anymore). My apache was bombarded with proxy requests and I could barely load up any of my websites (this blog included) from both internal network as well as from outside. So, I started to search the web in hopes of finding people with similar problems and their solutions. Here is what I have found on this website: