Lots of ways they could find that URL. Off the top of my head:
someone could have bookmarked the URL on one of the social bookmarking sites...they get crawled all the time.
Your servers log files (some server side log file programs are easily crawlable).
and as you said, someone could have linked to that page on their site...referenced it in a forum, etc...and no, people will generally link to the whole URL unless they are very web savvy and know that the variables are simply analytics information.
and no, people will generally link to the whole URL unless they are very web savvy and know that the variables are simply analytics information.
Both pages are live with the same content: example.com/widget/?pk_campaign=adwords&pk_kwd=keyword example.com/widget/
More people visit example.com/widget/ therefore it is more likely to be linked to or bookmarked than example.com/widget/?pk_campaign=adwords&pk_kwd=keyword.
example.com/widget/ is linked to inter-site so crawling the site should provide them with that page over the adwords version.
Lots of ways they could find that URL
yep, but many times the simplest explanation is to correct one, here the simplest explanation is that bing discovered the url via adwords and based on the url variables it was through google search or partners, not a content ad.
I just noticed this as well. They're using my AdWords campaign link instead of a link to my main site. The only way they could have collected this URL is from AdWords. The question is whether they're getting it from the ad network or if they're scraping Google's SERPs.
I had the same problem. Inside Site Explorer it was displaying a bunch of folders with ?'s at the end. When I clicked into them I realized that Bing was marketing them as unique pages and diluting my SE Results. Realizing my url parameters were not set up. I quickly migrated the settings from Google Webmaster over :)