Site authorization is an optional feature that allows you to identify only specific sites that you wish to display your ads on. If you are particularly concerned about malicious use of your ad code by others, you may wish to use this feature as a precaution.
Authorizing your sites
- Sign in to your account.
- Visit the Account settings tab.
- In the "Access & authorization" section, next to "Sites authorized to show ads," click edit.
- Check the box marked Only authorize certain sites to show ads for my account.
- Enter the URL of the site that you want to authorize and Save
Your changes should take effect within 48 hours.
What happens to sites I don't authorize?
If a URL displaying your AdSense ad code is not on your list of authorized sites, ads will still show on that URL, and impressions and clicks will be recorded. However, advertisers will not be charged, and you will not receive any earnings for that site.
If you don't add a site to the authorized sites list, and you place your ad code on it, ads will continue to appear on the site but you won't earn from them. So please enable this feature with caution to avoid missing out on valid revenue.
Sources : Google Reader