From the Bing Blog:

You may have read our post last week where we talked about how Smart Motion Preview and SafeSearch work together.

As we mentioned, Microsoft is never done when it comes to providing tools to help customers, whether they are large enterprises, local school districts or parents make sure they can provide a safe searching experience when using Bing.

We made two changes that we think will help.

First, potentially explicit images and video content will now be coming from a separate single domain, explicit.bing.net.  This is invisible to the end customer, but allows for filtering of that content by domain which makes it much easier for customers at all levels to block this content regardless of what the SafeSearch settings might be.  This makes it much easier for filtering software to block unwanted content if SafeSearch has been turned off.

In addition, we will begin returning source url information in the query string for images and video content so that companies who already use this method of filtering will be able to catch explicit content on Bing along with everything else they are already blocking for their customers.  An example of such a query string is:  

http://ts2.explicit.bing.net/images/thumbnail.aspx?q=974382499649&id=12ae77a7fed979b0502840bedacd2552&url=http%3a%2f%2fwww.explicitsite.com%2fexplicit-picturegoeshere.jpg  

Thank you to everyone who shared feedback with us on this matter, it helped us to quickly develop a solution and get it into production.

Mike Nichols, General Manager, Bing