SAN JOSE, Calif. — In its biggest threat yet against open-source software users, Microsoft said yesterday that open-source programs, including Linux, infringe at least 235 of the Redmond, Wash., software company's patents.

The company's statement was only the latest in a yearslong succession of vague warnings of potential lawsuits against businesses that sell and use open-source software, programs that are freely available for anyone to download and change.

Yet the numbers that the company released, first reported in Fortune magazine and confirmed by the San Jose Mercury News, were the first specific figures issued by Microsoft on open-source patents.

Without detailing individual claims, Microsoft contended that open-source programs infringed dozens of patents, including 42 in the kernel of the Linux computer operating system and 45 in the Microsoft Office-like productivity suite Open Office.

"Even the founder of the Free Software Foundation, (open-source advocate) Richard Stallman, noted last year that Linux infringes well over 200 patents from multiple companies," Horacio Gutierrez, Microsoft's vice president of intellectual property and licensing, said in a statement. "The real question is not whether there exist substantial patent-infringement issues, but what to do about them."

Once dismissed as geeks-only software, open-source programs are now sold by major technology players such as Hewlett-Packard and IBM, and used by corporate giants like Wal-Mart and Goldman Sachs, forcing Microsoft to grapple with open source as a legitimate competitor to its software businesses.

In fall 2006, the company struck a technology and licensing deal with once-bitter rival Novell to help customers who used both Microsoft products and Novell's Suse Linux, shielding Novell and its clients from patent claims. As part of the agreement, Microsoft promised not to sue open-source hobbyist programmers.

"Microsoft and Novell already developed a solution that meets the needs of customers, furthers interoperability, and advances the interests of the industry as a whole," Gutierrez said. "Any customer that is concerned about Linux (intellectual property) issues needs only to obtain their open-source subscriptions from Novell."

In March, the Free Software Foundation released the latest draft version of the GNU General Public License, which governs distribution of Linux and other open-source software. It contained language that might nullify the Microsoft-Novell deal. The final version, known as GPLv3, is to be released in the summer.

"The latest draft of the GPLv3 attempts to tear down the bridge between proprietary and open-source technology ... ," said a Microsoft spokesman.