US law requires an age verification page for when someone visits a web page about pornography, alcohol or other adult oriented pages. But this comes with a challenge for webmasters who want to make sure those pages are accessible to search engines.
For example, if you search for vodka one of the top results is for absolut.com, and if you click on it and in your in the US, you are taken to absolut.com/us and it pops open an age verification box. At the same time, absolut.com has over a thousand pages indexed in Google, how so?
A Google Groups thread has a response from a Googler on how to handle these situations. Susan Moskwa of Google said:
This topic comes up periodically for sites (alcohol, porn, etc.) that need to serve an age verification notice on every page. What we recommend in this case is to serve it via JavaScript. That way users can see the age verification any time they try to access your content, but search engines that don't run JavaScript won't see the warning and will instead be able to see your content.
Google won't run the JavaScript request and GoogleBot will simply bypass that page and crawl the site. Of course, what if JavaScript is turned off on a child's browser?
Forum discussion at Google Groups.