Now, this is important.
If you have a website which contains some Password protected pages, like login account pages. then you must read what I have to say.
AdSense has a powerful crawler, which crawls through your blog/site and searches for the most repeated or similar contents. now when the search ends and the crawler provides the information to ad units. this is how you ads on adsense are targetted.
Now, if you have some password protected pages on your blog/site. What will happen? when adsense crawler reaches those pages, it obviously can't get access to those pages, thus your content on those pages is never been crawled and you wont get any relevant ads on those pages.
Now that is trouble, if there are no relevant ads, that means less clicks and that means less earnings.
So, What should you do ?
Google have recently launched a new feature called Site Authentication to take care of this problem. Using Site Authentication, you can give our crawler access to your login-protected pages by passing it information to log into your site.
To get relevant Ads on those pages, you can use Site Authentication to provide AdSense crawler with a test username and password. It's an easy process:
* log into your AdSense account.
* find the 'Site Authentication' link under the 'AdSense Setup' tab.
Once you've supplied us with a username, password, and a few other details, all you have to do is verify that you own the site through Google Sitemaps.
If you need additional help, feel free to visit Adsense Help Center. Once you've set up your authentication rule and verified ownership, it may take 1-2 weeks for Adsense crawler to visit your site again.
Your users will thank you, and so will the AdSense Crawler.