The default is that your search text gets sent to Microsoft and not, AFAIK, to advertisers directly. I can definitively say that at the very least, Microsoft ha

The default is that your search text gets sent to Microsoft and not, AFAIK, to advertisers directly. I can definitively say that at the very least, Microsoft has established a firm barrier of separation between the advertisers and the Windows client. For example, it's not just a web page with embedded advertiser's javascript/html that it displays when you get your search results, everything is curated by Microsoft and delivered by their servers.