The article in the WSJ insinuates that it can come from either IE or the toolbar:
Stefan Weitz, director of the Bing search engine at Microsoft, said in an interview the company studies how certain users interact with Google in order to improve Bing. It does this by looking at "clickstream data," or information that users of Microsoft's Internet Explorer or the Bing search toolbar voluntarily share with the company
Stefan Weitz, director of the Bing search engine at Microsoft, said in an interview the company studies how certain users interact with Google in order to improve Bing. It does this by looking at "clickstream data," or information that users of Microsoft's Internet Explorer or the Bing search toolbar voluntarily share with the company
source: http://online.wsj.com/article/SB1000142405274870412450457611...