The Web-search giant, Google, has accused the software giant, Microsoft, of breaching a US legal settlement that was supposed to reduce the dominance of the Windows operating system, according to US media reports.

Quoting sources familiar with the case, Wall Street Journal said Google had filed a 50-page complaint in April with the US Department of Justice over desktop searches,

a software that allows a personal computer user to rapidly find information on their own hard drives. Google offers a program to do this, and so does Microsoft as part of Windows Vista.

„Microsoft’s current approach with Vista desktop search violates its agreement with the government and hurts consumers. The search boxes built throughout Vista are hard-wired to Microsoft’s own desktop search product, with no way for users to choose an alternate provider from these visible search access points. Likewise, Vista makes it impractical to turn off Microsoft’s search index,” a Google spokesman reportedly said.

According to the newspaper, Google has been in talks with the Department of Justice on the issue for one year, but analysts said the complaint was likely a riposte to a separate legal challenge from Microsoft against Google's alleged dominance in advertising.

Bradford Smith, the general counsel at Microsoft, told the New York Times that the company was unaware of the memo. He told the newspaper that Microsoft had not violated the consent decree and that it had already made modifications to Vista in response to concerns raised by Google and other companies.

Microsoft has asked anti-trust authorities to prevent Google's acquisition two months ago of DoubleClick.