The top lawyer for Microsoft Corp. claims free and open-source software infringes on more than 235 of the software giant's patents, according to a magazine report published Sunday.

Microsoft general counsel Brad Smith told Fortune magazine the heart of open-source software, the Linux kernel, violates 42 Microsoft patents, while Linux's user interface and design violates another 65 patents.

Smith also alleged OpenOffice — a suite of programs providing similar services to Microsoft Office — violated 45 patents, while another 83 patents could be found in other free and open-source programs, according to Fortune.

It's the first time someone at Microsoft has revealed how many of its patents it believes open-source software has violated.

Microsoft's programs, such as Windows or Office, run on proprietary source software, meaning the underlying computer code is restricted and guarded by patent and other intellectual property protections.

Open-source software such as Linux, on the other hand, encourages access to its basic code.Individuals are free to add to or modify the software without fear of legal repercussions, as long they abide by the conditions of the General Public License, which stipulates that the program must remain open and sharable.

A number of companies — including Sun Microsystems, Red Hat Inc. and Novell Inc. — run versions of Linux.

Smith and Microsoft head of intellectual property and licensing Horacio Gutierrez did not provide any details to Fortune about how they might proceed in enforcing these patents, and did not name any of the patent infringements specifically. A call to Microsoft was not immediately returned.

In November, Microsoft took another route, negotiating a deal with Novell that included an agreement to provide each other's customers with patent coverage for their products and pledging that neither company will make patent claims against their rivals' customers.

Supreme Court decision makes patents harder to get

The legal landscape for technology patents remains a muddled, but increasingly high-stakes, area in the United States.

A U.S. Supreme Court decision on April 30 made it more difficult to obtain patents based on previous inventions.

"Granting patent protection to advances that would occur in the ordinary course without real innovation retards progress and may … deprive prior inventions of their value," Justice Anthony Kennedy wrote in his ruling in the case of KSR International Co. v. Teleflex Inc.

The case did not deal with software but rather the design of an adjustable gas pedal. But a number of technology heavyweights, including Intel, weighed in with filings arguing that combinations of existing inventions should be ineligible for patent protection.

The U.S. Patent and Trademark Office awarded 40,964 software patents in 2006, an increase of 36 per cent from the previous year, according to an analysis of data conducted by the Public Patent Foundation earlier this year.

With files from the Associated Press