The Mountain View-based search giant says Microsoft's Bing has been monitoring what people search for on Google and then mirrors those results on its own page.
The head of Google's web spam took to Twitter to announce that his company would be taking Microsoft head-on over the accusations.
(Google's head of search, Amit Singhal is a guest on "Press:Here" this Sunday, Feb. 6.)
While not denying the accusation, Harry Shum admitted that his company monitors some Google users' activity to improve Bing's own search.
"We use over 1,000 different signals and features in our ranking algorithm," he wrote on his blog. "A small piece of that is click stream data we get from some of our customers, who opt-in to sharing anonymous data as they navigate the web in order to help us improve the experience for all users."
Shum was also scheduled to speak at the same conference in San Francisco Tuesday as Cutts.