Microsoft and Google are squaring off again over alleged anti-trust violations.

In a leaked Department of Justice (DoJ) filing, Google reportedly claimed that the desktop search features in Windows Vista favoured Microsoft's proprietary software over third-party applications such as Google Desktop.

The move violates the terms of the landmark 2002 antitrust settlement, according to Google, in which Microsoft agreed not to use its position as the dominant PC operating system vendor to promote its other products.

Microsoft chief executive Steve Ballmer was quick to dismiss the filing, referring to the complaints as "baseless".

"We continue to comply with the consent decree we signed with the US government in recognition to the findings around our position with Windows," he told reporters.

Ballmer appears to have the backing of at least one member of the DoJ. The New York Times reported that assistant district attorney Thomas Barnett sent a memo urging state attorneys general not to pursue the case against Microsoft.

Google would not specifically respond to Ballmer's remarks, but a spokesperson provided vnunet.com with a statement explaining the company's position.

"Microsoft's current approach with Vista desktop search violates the consent decree and limits consumer choice," read the statement.

"The search boxes built throughout Vista are hard-wired to Microsoft's own desktop search product, with no way for users to choose an alternative provider from these visible search access points."

Google and Microsoft have been trading antitrust accusations for more than a year. In May 2006, the search giant lobbied the DoJ and the European Union , claiming that Internet Explorer 7 unfairly directed users towards Microsoft's MSN Search.

Microsoft has made antitrust accusations of its own against Google, most recently concerning Google's purchase of ad firm DoubleClick.