The barbs are injecting more hostility into already bitter rivalry between world’s most powerful tech companies.

Google’s search engine is dominant on the internet while Bing runs a distant second. Microsoft’s office and Windows remain an integral part of personal computers but Google’s successful web based services and Android OS are seeing to it that Microsoft losses its dominance in these areas too.

According to the latest data from StatCounter, Google leads the search engine market with a whopping 90.47 percent in January 2013, while Bing managed to rake in only 3.33 percent.

Google however doesn’t require websites to pay to be listed in its main database; hence quarries of any products will display the results that still include the merchants who haven't paid for the privilege of being included.

But that's not the case for someone who clicks on a tab to enter Google's shopping-only section, which is designed to compare prices and offer other insights such as identifying sites that offer free shipping. That means results from sites, including Web retailing giant Amazon.com, aren't displayed unless they pay.

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

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