Consumers who purchased Microsoft software indirectly cannot sue the software company in federal court for claims related to the US Department of Justice's antitrust suit.

The US Fourth Circuit Court of Appeals came to the decision in the Kloth versus Microsoft case. It dismissed all the case's claims, which were attempting to create a class action for people who purchased Windows, Word and other Microsoft software during the 90's but did not buy it directly from Microsoft.

The decision affirmed a lower-court decision made previously by Maryland District Court Judge J. Frederick Motz, stating that a consumer class of indirect purchasers may not recover alleged overcharges by Microsoft, said Mark Murray, a Microsoft spokesman.

Murray called the decision of the appellate court "a significant milestone for Microsoft".

"This ruling essentially marks the end of this case," Murray said. However, the plaintiffs can appeal to the US Supreme Court.

Microsoft has already settled a number of class-action suits with individual US states, resulting in the vendor agreeing to pay out millions of dollars to purchasers of its software in each state. Some state cases are still pending.

The plaintiffs in the federal class-action suit had bought hardware from OEMs (original equipment manufacturers) or retailers on which the software was already installed. They argued that even though they were indirect purchasers, they still had a "direct economic relationship" with Microsoft, according to court papers filed Tuesday. Therefore, they argued that Microsoft caused them direct injuries by suppressing competitive technologies, restricting the terms of end-user licenses and degrading computer performance, according to the filing.