What does this from Google mean in your traffic stats

I've been puzzled by this for a very long time now after seeing it in traffic stats for "last visitors." The "last visitor" is often this ("Example.com = your site"):

http://www.google.com/url?url=Example.com&yahoo.com

Does anyone know for sure exactly what that means? What is the source of the traffic? Why does it appear that way? Why does it mention Yahoo.com at the end?

 

This is a example of Google analytics spam traffic. You can filter these type of traffic.