According to several sources, Microsoft has been very naughty with its bing search engine results. In a controlled experiment by Google, the search engine leader placed bogus results for random strings of characters into its results page, which promptly turned up in the bing results page for that same string of characters. It seems that Microsoft was using data gathered from the search bar in Internet Explorer to query Google and then put the results into its bing search index.
An analogy would be recording conversations you were having with a favourite supplier, then using the information to supply an identical service.
Microsoft puts it differently, attempting to explain that it was legitimately drawing information from a variety of sources.