Linus Torvalds has joined the chorus of voices speaking out against software patents.

"Software patents are clearly a problem, and I think it's a problem that the open source community has been pretty aware of for the last five years," said Torvalds. "The good news is that a lot of proprietary vendors are starting to see it as a problem as well."

He was referring to announcements by IBM and Sun last month that they will make thousands of software patents available to open source developers. IBM made 500 of its patents available to the open source community, saying it would promote innovation. Sun followed suit two weeks later, releasing more than 1,600 patents of its own.

More companies are expected to follow, but nevertheless, patents remain a major source of concern, according to a panel of open source luminaries who discussed the issue at the OSDL Enterprise Linux Summit in California.

There are an estimated 150,000 to 300,000 registered software patents in the US alone, and many open source developers would like to see them invalidated. They believe that many such patents are frivolous and that copyright law is a better mechanism for protecting software innovations.

Part of the problem is that the US Patent Office has been lax in granting patents, said Mitchell Kapor, a founder of Lotus Development and a prominent backer of the Mozilla browser. "There have been tens of thousands of bad software patents issued which never would have been issued if the Patent Office had actually been following its own rules," he said.

Ultimately, these bad patents may come back to haunt the open source community, Kapor predicted, saying that Microsoft will eventually be driven to launching wide-ranging patent lawsuits, which he called "patent WMDs" against open-source projects. "Their business model no longer holds up in an era where it's clear that open source is simply an economically superior way to produce software," he said. "Of course they're going go unleash the WMDs. Why would they not?"

Torvalds was reluctant to make predictions though. "I'm the anti-visionary. I distrust people with visions," he said. "You don't see what's right in front of your face and you don't see the technical issues that face everyday users."