San Francisco - Microsoft is trying to skewer Google as a lousy holiday shopping guide in its latest attempt to divert more traffic to its Bing search engine.

The attack started Wednesday with a marketing campaign focused on a recent change in how Google runs the part of its search engine devoted to shopping results. The revisions require merchants to pay Google to have their products listed in the shopping section.

In its new ads, Microsoft Corp. contends the new approach betrays Google Inc.'s longstanding commitment to provide the most trustworthy results on the Web, even if it means foregoing revenue. To punctuate its point, Microsoft is warning consumers that they risk getting "scroogled" if they rely on Google's shopping search service.

The message will be highlighted in TV commercials scheduled to run on NBC and CNN and newspaper ads in The New York Times, The Wall Street Journal and The Washington Post. The blitz also will appear on billboards and online, anchored by a new website, Scroogled.com.

The barbs are likely to inject more antagonism into a bitter rivalry between two of the world's best-known and most powerful technology companies.

Google's search engine is dominant on the Internet, with Bing running a distant second. Microsoft's Office and Windows software remains an integral part of personal computers, but Google has been reducing the importance of those programs and PCs with the success of Web-based services and its Android operating system for smartphones and tablet computers.

Google still doesn't require websites to pay to be listed in in its main database. That's the index providing the results for requests entered into Google's all-purpose search box. A query made there for a particular product, such as computers, will still include results from merchants who haven't paid for the privilege of being included.

But anyone who clicks on a tab at the top for shopping-specific results will see only listings for paying merchants. That means results from sites, including Web retailing giant Amazon.com Inc., aren't displayed unless they pay. Amazon so far has only occasionally paid to have some of its wares listed in Google's shopping section. Zappos, a site owned by Amazon, has been more willing to pay the price to be listed in Google's shopping results.

Google defends the fee-based approach as a way to encourage merchants to provide more comprehensive and accurate information about what they're selling.

"I think you just get a well-organized set of product information, ways to buy it, and really have a great experience there," CEO Larry Page said during a conference call with analysts last month.

In a statement late Tuesday, Google said it's pleased with the response to the new shopping system, which offers listings from some 100,000 sellers.

Google, like Microsoft, also accepts payments for ads that are triggered by specific search terms and appear to the right or on top of regular search results. Those are labeled in gray letters as ads.

Since mid-October, Google's shopping section has included only listings from merchants who paid to be included in the results. In some cases, the order of the shopping results has been dictated by how much money Google received for the listing. The change coincides with what is expected to be the most lucrative holiday shopping season on the Web yet.

Google discloses that it receives payments in small print at the bottom of the shopping results page. The notice is also visible if a user clicks on a link at the top of the shopping results page, under the heading: "Why these products?"