Microsoft (NasdaqGS: MSFT - news) has launched a new website accusing Google (NasdaqGS: GOOG - news) 's online shopping search engine of only showing results from paid advertisers - but it may be guilty of the practice itself.
Stepping up the battle between the tech giants, Microsoft created "Scroogled" as part of the latest marketing campaign for its own search engine Bing.
Microsoft claims its rival has reversed its pledge at the time of the Google stock offering to avoid paid ad inclusion for search results.
It says it is seeking "to help explain to consumers the risks of Google Shopping's newly announced 'pay-to-rank' practice.
"Google Shopping is nothing more than a list of targeted ads that unsuspecting customers assume are search results."
It said the campaign was "to highlight Bing's commitment to honest search results".
Google announced earlier this year that it would revamp its product search to become a shopping service with paid listings.
This eliminated merchants which opted not to pay, including some notable ones like Amazon.
Google said it completed the transition on October 17 in the US, and would be rolling out the same model in the UK, Germany, France, Japan (EUREX: FMJP.EX - news) , Italy, Spain, The Netherlands, Brazil, Australia and Switzerland.
"We think this will bring the same high-quality shopping experience to people - and positive results to merchants - around the world," Google said in a blog posting.
Google maintains that merchants cannot improve their rank simply by paying more, and sellers who have a financial stake in the results will keep their information up to date.
"Google Shopping makes it easier for shoppers to quickly find what they're looking for, compare different products and connect with merchants to make a purchase," said a Google spokeswoman.
However, some analysts say both companies are less than transparent about how their shopping engines work - and Microsoft is not without blame.
Danny Sullivan, an analyst for Search Engine Land, said of the Microsoft effort: "Great campaign, if it were true. It's not. Bing itself does the same things it accuses Google of."
He explained: "At least Google has the fine print that you can read; Microsoft doesn't have it at all."
Microsoft, according to Mr Sullivan, excludes new merchants from Bing search results if they do not pay for inclusion with its partner, Shopping.com, even though this is not fully transparent to consumers.
"Payment is a factor for ranking (in Bing)," he said, insisting Microsoft's campaign is misleading.
Microsoft said its own shopping results through Bing were not influenced by payment.
"Bing includes millions of free listings from merchants and rankings are determined entirely by which products are most relevant to your query," said senior director Stefan Weitz.
"While merchants can pay fees for inclusion on our third party shopping sites and subsequently may appear in Bing Shopping through partnerships we have, we do not rank merchants higher based on who pays us.
"Nor do we let merchants pay to have their product offers placed higher in Bing Shopping's search results."
Mr Sullivan said the overall message from the latest row is that consumers should shop around and use multiple search engines.
"All of them suggest that they are gathering stuff from across the web, but may not be doing that," he added.