How do I prevent this harmful porn sites

As a Ad sense publisher you need to adhere to a Ad sense Usage Policy. One such policy included within is about not showing your Ad sense Ads in websites which include Porn or violent content. However, even though you might not have any intentions of showing ads in such websites, its possible that your Ad sense Publisher ID gets used by tricksters for showing Ad-sense Ads in such websites. This though, wont give any straight benefit to the website publisher, but it can cause serious damage to my Ad-sense

 

Log into your adsense account.

You will find a section where you can click on Allowed Sites and add the sites where you want your ads to appear.

If someone places your ads elsewhere you will not be banned, plus you can proof to google that you never wanted your ads to appear on another website.

Here is a write-up on how to do this: http://www.commentaryweb.com/ppc-advertising/protecting-your-adsense-account/

 

Why would someone want to do that?

 

people can do that. if you are making 200 bucks a day with adsense, then obviously your competitors might want to get your source cut off. Like people do this to nail down compeitors on cl, youtube,blogger by false flagging etc

 

There are several dozens methods to screw someone else's adsense...

 

But, how would somebody be able to know another person's adsense code or account?

 

That is very easy. Just look at the source to find out.

 

First, any attempt I want to thank you
To answer my question