Microsoft has filed an appeal in the patent infringement case brought by Eolas Technologies, even though a US$520.6 million judgment against Microsoft was thrown out earlier this month.

Microsoft, in court documents filed 16 March, asked the US Court of Appeals for the Federal Circuit to overturn a portion of the Eolas web-browsing claim dealing with patent claims on foreign sales of Microsoft's Internet Explorer browser, This section of the claim had not been reversed when the court ordered a new trial on 2 March. Microsoft asked the court to strike down Eolas' argument that it should be awarded money based both on Microsoft's US and foreign sales, saying the Eolas patent only covers US sales.

Microsoft lawyers argued in the brief that US. patents should not apply to so-called golden master disks containing copies of software programs that are used by foreign computer makers to install software. The software code on the golden master is a set of instructions, not a component of a patented US invention, Microsoft's lawyers argued.

The court ruled that software code is the key part of the Eolas patent for technology that allows interactive content to be embedded in a website, a common practice on the Internet. But Microsoft's lawyers said the same case could be made for any invention's blueprint, although courts have required patent infringement claims on foreign sales to prove that components of an invention have been copied and sold.

"Every patented invention, at bottom, is the reduction to practice of a conception," wrote Microsoft lawyer Carter Phillips. "When the (court) says that software code is the 'key' to this invention, it is saying nothing more than that the description of how to practice an invention is 'key' to that invention."

Even though the appeals court ordered a new trial to determine the validity of the patent, the issue is an important one to clear up because many software companies use golden master discs, said Stacy Drake, a Microsoft spokeswoman.

The University of California, which spun off Eolas into a private company and joined it in the lawsuit, is confident the court will uphold its earlier ruling regarding foreign patent claims, said Trey Davis, director of special projects at the university. "We'd expect any future rulings would be a vindication for our position," he said.