Because Google's search results are so good, it's possible (and maybe even common nowadays) to use Google's rank(someQuery, someDocument) as a relevance label to train your own ranker on, but what Google alleged here is even more interesting: they claim Microsoft used IE to telemetrize users' Google searches, scraping the query and results -- `(someQuery, [document1, document2, ...])` -- phoning that home, and using that _directly as their IR_, presumably by caching it or something. Kind of a cheeky move by Bing!
Edit: Just checked and Chrome wasn't the dominant web browser until mid-2012 or so[0], so IE definitely would have seen a big enough share of Google searches to make this viable. I wonder if this factored into Google's strategy for Chrome and monopolizing search, etc.
[0] https://en.wikipedia.org/wiki/Usage_share_of_web_browsers#/m...
