Google's Atul Bhandari explained the feature on the AdSense blog, including:

General category blocking will allow you to block even more categories of ads from appearing on your site. We're testing this feature with 170 more specific categories, including finance, travel, job, and automotive. This feature will allow publishers to block up to 50 ad categories from among a broad range of 170 fine grained categories. To help you understand potential changes to your earnings, we'll provide you with the percentage of your total revenue and total impressions that fall under each category.

Bhandari says the blocking will only apply, at this stage, to ads in English, regardless of the language of the site. However, Google has stated that they are already working on expanding this feature to other languages in the coming days.

The new feature will demonstrate to the website publishers the effect on their earnings once they apply the new category blocking product (see image below).

AdSense users should be aware that not everyone will get to take advantage of the new options. General Category Blocking is only available through the new AdSense interface, which is currently still in beta. So for the time being only a limited number of publishers are able to test this feature.

The good news for AdSense publishers is that they now how more control on the types of ads that appear on their site. The news is not so good for AdSense advertisers. Google seems to have forgotten about the effect it will have on advertisers as this new feature limits the number of websites their ads can be featured.