The Redmond, Wash., software maker, which holds about 4,500 patents covering a broad spectrum of technology affecting desktops, servers, and more, said in December that it would begin licensing patents to meet requests from customers, partners, and regulators.
Microsoft has more than 100 discussions underway for patent licensing, according to the Wall Street Journal, which first reported on the concerns of the open-source community on Friday. The software maker is offering royalty-bearing licenses to any interested party, including makers of open-source products.
A Microsoft spokesman said in a statement released Friday that the company's intellectual-property policy was to encourage the "broader availability and use of technology developed from our nearly $7 billion annual commitment to R&D."
"This policy is well within industry norms set by companies like IBM, AT&T (Bell Labs), and others who have been licensing for nearly 50 years," the statement said.
Microsoft's position, however, failed to lessen the anxiety among open-source groups.
"We are very worried," said Eric Raymond, president of the Open Source Initiative, a nonprofit group that certifies open-source licenses. "This is aimed directly at us. It's a classic Microsoft attempt to crush the competition."
Microsoft executives have acknowledged publicly that Linux, an open-source operating system, is a serious competitive threat, particularly in computer servers used to run business applications. Linux also has made inroads against Microsoft Windows on the desktop, particularly in countries outside the United States.
But issues surrounding Microsoft's new approach to its use of patents go beyond market competition, open-source supporters said. The larger issue is the failure of the U.S. Patent and Trademark Office to approve software patents for real innovations, as opposed to commonly used techniques.
"We have a patent-quality problem," Daniel Ravicher, executive director of a nonprofit group called the Public Patent Foundation, said.
Ravicher claimed that about half the patent-infringement cases involving software that go to court end with the patent being proven invalid. An additional 25 percent end with the finding that there was no infringement, he said.
Large Linux distributors, such as IBM, have the legal resources to handle patent disputes, Ravicher said, but far smaller organizations building open-source applications wouldn't have the money to fight Microsoft in court.
"I don't think IBM is worried, but the Apache Software Foundation and the Free Software Foundation are," Ravicher said, naming the latter two organizations as examples.
Mark Webbink, legal counsel for Red Hat, the largest independent Linux distributor, said he didn't know whether Microsoft's patent approach would have an impact on the company.
"To have an impact, you have to have something that's subject to one of [Microsoft's]patents, and they have not given us any notice of that," Webbink said.
The attorney, however, acknowledged that there's an "inherent structural problem" in the system for issuing software patents.
Part of the problem is the relative youth of the commercial-software business, in comparison with older industries, like steel or manufacturing. Until the early 1980s, for example, there was no copyright or patent protection for software, Webbink said.
Therefore, there isn't enough recorded history for the U.S. Patent and Trademark Office to use in deciding whether an applicant's code reflects true innovation.
"As a result, we end up with a lot of litigation," Webbink said.
Among the largest copyright cases involving open-source software to date is a multi-billion-dollar suit filed by SCO Group against IBM. The Utah software company claims IBM inserted SCO's copyrighted Unix code into Linux. IBM has denied the charges and has counter sued.