I confess that I'm puzzled. I don't think that the ad is "from" AW. Our ad lists do not list Nordstroms. The way the ad functions is such that it violates the contracts our ad services have with us and with ad providers.
The ad in question:
1. Is a Nordstrom ad for shoes or frangrance.
2. The ad appears in a new tab.
3. The ad appears either from after clicking a New Posts link or clicking on a thread title (1 instance).
4. The ad appears for users on OS X and various flavors of Windows, using Firefox and Safari.
5. I've been using Firefox and Safari and trying to get the ad to display. I can't.
6. I can't find a link on AW that plants a redirect cookie, or a similarly functioning graphic or webbug.
7. Logging off, deleting cookies, emptying the cache and history seem to solve the problem temporarily, but the ad returns a day or two later.
At this point I'm wondering about one or more other sites planting the redirect that is then triggered while browsing AW because the people seeing the ad are all regular readers of AW.
It is happening elsewhere; I'm on touch with a number of other admins with the same concerns and no answers. None of the other sites I know of that are seeing the ad are writing sites, or I'd point to a common writing site as the vector.
It's not dangerous or malicious as far as I can determine, just annoying, and I don't like it happening to AW members.