Google has been increasingly punishing of mobile sites that contained any sort of annoying pop-up interstitials and continues the purge of obnoxious advertisements through their change in policies. Recently, Google updated its policies regarding popups, but not just any popups. They’re targeting what Google describes as “pop-under” ads, or advertisements that people cannot see until they minimize their window. If you’d like to read the entire announcement, you can find it here.

Here’s a quick rundown of the changes that Google is making:

1. Publishers are not permitted to place Google ads on sites which have more than three pop-ups. If pop-ups are displayed on a site, they may not interfere with site navigation, change user preferences, initiate downloads, or distribute viruses.

2. Publishers are not permitted to place Google ads on sites that contain or trigger pop-unders.

3. Additionally, sites using AdSense may not be loaded by any software that triggers pop-ups, modifies browser settings, redirects users to unwanted sites, or otherwise interferes with normal site navigation. It is your responsibility to ensure that no ad network or affiliates use such methods to direct traffic to pages that contain your AdSense code.

4. Publishers are not permitted to place Google ads in any window that is not initiated by an intentional user interaction (e.g., click). Additionally, Google ads may not be placed in any web browser window that lacks navigational controls, including back and forward browsing buttons, and an editable URL field.

Note that Google is not saying that they are demoting sites with pop-under ads, but instead updating their Adwords Guidelines.