Microsoft's Bing search engine is the first serious competitor to Google in over a decade, but now Google says that Bing is copying its own search results, and that the company has run tests that prove it.
Google first smelled a rat when misspelled searches on Bing would bring up the same spelling corrected results as a Google search, even though Bing didn't attempt to correct the misspelled search term. Then Google noticed a stronger than expected correlation between the top 10 results for many searches.
So the company ran a sting, where it created "synthetic" searches by adding a random letter and number series to various web pages. A Bing search for that series returned no results until it was manually added to Google's search results, at which point it would magically appear in the Bing search.
Bing hasn't actually denied Google's claim, saying only that they use "multiple signals and approaches" to generate results. For its part, Google likens this to copying off your neighbor's paper during a school test, then saying that you just wanted to get a better grade.