Microsoft has denied claims Bing results were directly copied from Google, as the two tech giants came to blows.
Google claimed it had seen various URLs from its own search results appear in Bing "with increasing frequency for all kinds of queries."
These included popular, rare, unusual and misspelled queries, Google claimed.
"Even search results that we would consider mistakes of our algorithms started showing up on Bing," Amit Singhal, Google Fellow, said in a blog post.
"We couldn't shake the feeling that something was going on, and our suspicions became much stronger in late October 2010 when we noticed a significant increase in how often Google's top search result appeared at the top of Bing's ranking for a variety of queries."
Google then carried out an experiment, creating around 100 "synthetic queries" searches users would not be expected to carry out, like random word jumbles.
Google gave 20 engineers laptops installed with Microsoft Windows running Internet Explorer 8 with the Bing Toolbar added.
Furthermore, the IE8's 'Suggested Sites' feature was added and default options for the Bing Toolbar were used.
"We asked these engineers to enter the synthetic queries into the search box on the Google home page, and click on the results, i.e., the results we inserted," Singhal explained.
"We were surprised that within a couple weeks of starting this experiment, our inserted results started appearing in Bing."
He claimed that some Bing results increasingly appeared "like an incomplete, stale version of Google results - a cheap imitation."
Microsoft has fobbed off Google's claims, offering its own blog post from Harry Shum, corporate vice president of Bing.
He explained the firm receives clickstream data from some users who opt-in to sharing anonymous data which will then go into improving search results.
Shum said Google had not accurately portrayed how Microsoft uses opt-in customer data "as one of many inputs to help improve our user experience."
"We use multiple signals and approaches in ranking search results," said Stefan Weitz, Microsoft director of Bing, in a statement sent to IT PRO.
"The overarching goal is to do a better job determining the intent of the search so we can provide the most relevant answer to a given query. Opt-in programs like the toolbar help us with clickstream data, one of many input signals we and other search engines use to help rank sites."
Microsoft also had a mini-spat with Yahoo this week, after it said the latter's mail offering was to blame for Windows Phone 7 'phantom data' leakage.
Now Yahoo has responded by saying the problem had not affected any other devices on which its mail service runs and was specific to Windows Phone 7.
