Google Adsense: How to Block the Competitors Ads?

Recently, we have seen the incidents wherein competitors ads are appearing on some of the web portals. For example, an Ibibo ad appearing on Yaari's website and Mypopkorn ads appearing on BigAdda, All these Ads were displayed using Google adsense. I just wanted to make this posting to let people know that there is way to block the competitor's ads on their webpages and how to use it on google adsense.
Basically while setting up the Adsense unit, there is an option called Competitve Ad Filter under Adsense Setup. In Competitve Ad Filter you can mention the url of your competitor whose ads will be blocked on your site. So Basically if Yaari.com wants to block Ibibo.com ads then they can just mention ibibo.com as one of the url in competetive ad filter. But Ibibo still has way to show up its ads on yaari using a hack. Google blocks the ads based on the destination domain name, so if I create an Ibibo ad which points to say xibibo.com which again gets redirected to ibibo.com then Google will not block such ads. Alternate way is to use Allowed Sites option under Adsense setup tab where you can mention the list of domain whose ads can appear on your site. People using Google adsense should use these features of Adsense and at same time keep adding the competitors domains to the compettetive ads.
The domain names used are just for example and this post is not meant to malign there image.