You may have seen this after logging in to your AdSense account…
Your ads have recently appeared on websites you haven’t authorized. To avoid lost revenue, make sure to authorize any sites where you display ads by visiting your account settings.
When you click the link you’ll find various sites and IP addresses that have been displaying your ads. Some of the sites and IP’s are simply cached search engine URLs and some are not so clear.
I always thought it was strange to see Google’s domains in this list. Why don’t they recognize their own URLs? So I did some digging around and found this article on the Google AdSense Support page:
When using the authorized sites feature, any sites that you haven’t authorized will trigger an alert message on your home page. We currently consider any framed or cached pages to be unauthorized, including when a user searches using Google Images and your site is displayed via frame.
We encourage you to add framed and cached URLs of sites you trust to your authorized sites list. We’re investigating ways to improve this feature.
So I would “allow” all domains that you trust (Bing, Yahoo, Google cache, Google translator, etc.) Now that I understand this is an automated issue from caching and frames, it makes a little more sense why certain sites are showing up in the alert.
Maybe they should consider putting this explanation on the actual page with the alert. I’m sure this has confused quite a few publishers.