Understandably, there's been a lot of hand wringing about this. But the experts and evidence all suggest that Microsoft is all bark and no bite in this particular case.
Let's start with the study that Steve Balmer likes to tout, claiming it shows that even Open Source advocates acknowledge that linux massively infringes on patents. Dan Ravicher, the author of the study and well-known anti-patent warrior, has come out saying that, in fact, the study proves the opposite of what Balmer claims it does:
"Open source faces no more, if not less, legal risk than proprietary software," Ravicher told technology news site eWeek. "The market needs to understand that the study Microsoft is citing actually proves the opposite of what they claim it does.
"There is no reason to believe that GNU/Linux has any greater risk of infringing patents than Windows, Unix-based or any other functionally similar operating system. Why? Because patents are infringed by specific structures that accomplish specific functionality."....
Ravicher said the crucial difference between his report and Ballmer's use of it was in the distinction between potential and actual patent violation.
"Ballmer makes a very bold statement by saying Linux infringes hundreds of patents," Ravicher said. "That is extremely different than saying 'Linux potentially infringes x patent', because the requirement to prove infringement is much more difficult than the requirement to simply file a case claiming infringement.
"He misconstrues the point of the OSRM study, which found that Linux potentially, not definitely, infringes 283 untested patents, while not infringing a single court-validated patent."
Then there is the point brought up by a number of folks but most eloquently expressed by Linus Torvalds that Microsoft's unwillingness to say exactly what patents linux violates is a clear sign that they know they have a weak case:
"Naming them would make it either clear that Linux isn't infringing at all (which is quite possible, especially if the patents are bad), or would make it possible to avoid infringing by coding around whatever silly thing they claim," he said.
"So the whole, 'We have a list and we're not telling you,' itself should tell you something," Torvalds said of Microsoft's stance in the Fortune story. And for good measure, he added: "Don't you think that if Microsoft actually had some really foolproof patent, they'd just tell us and go, 'nyaah, nyaah, nyaah!'"
"It's certainly a lot more likely that Microsoft violates patents than Linux does," said Torvalds, holder of the Linux trademark. If the source code for Windows could be subjected to the same critical review that Linux has been, Microsoft would find itself in violation of patents held by other companies, said Torvalds.
"Basic operating system theory was pretty much done by the end of the 1960s. IBM probably owned thousands of really 'fundamental' patents," Torvalds said in a response to questions submitted by InformationWeek. But he doesn't like any form of patent saber rattling. "The fundamental stuff was done about half a century ago and has long, long since lost any patent protection," he wrote.
Then there's this post from a well-known patent blogger who claims to have worked for Microsoft trying to figure out how to squeeze money out of linux via patents:
Microsoft spent years figuring out that Linux infringed, it asserts, 235 Microsoft patents. Patent Hawk worked on the project years ago, by the way. The problem was how to make money off the infringement. Just settling its U.S. antitrust suit, Microsoft wasn't willing to soil its reputation with lawsuits.
Linux software is covered under the GNU General Public License (GPL), a savvy scheme cooked up by Richard Stallman, intended to keep the software in the public domain. The GPL license prohibits Linux distributors from cutting a straight patent deal with Microsoft.
Novell worked around GPL by striking a very peculiar deal with Microsoft, agreeing not to sue each other's customers for patent infringement, and a marketing collaboration that put $348 million of Microsoft money in Novell's pocket in return for a cut of Novell's Linux revenue through 2011, and with Microsoft handing out coupons for Novell Linux. The move satisfied corporate Linux patrons like IBM and HP, but hacked off the free software developers who sweat over a hot keyboard cranking out the open-source code.
Stallman, meanwhile, came up with a revised GPL, presumably effective this coming July, that will waive the right of Microsoft, as a Linux distributor (via its coupons), to sue any Linux user for patent infringement. Microsoft says that handing out coupons doesn't bond it to the GPL. Regardless, the new GPL will prevent other Linux distributors from striking a deal with Microsoft like Novell did; which leaves Microsoft, seemingly barred from another fandango a la Novell Linux, holding its patents like roses, trying to sweet talk direct licenses from Fortune 500 Linux users, an approach that, to date, has met with very limited success.
Last but certainly not least is the very real threat that Microsoft would likely be counter-sued for infringement by some very big players if they really went after linux. Companies including IBM, Sony, Philips, Novell, RedHat, and Oracle all participate in a linux-protecting patent pool project called the Open Invention Network. And while the group doesn't explicitly promise to go after anyone who sues a stakeholder for linux patent infringement (the point is more to contribute patents that they promise not to assert against each other as long as members don't assert patents against linux), the clear implication is that members are contributing chits to be used in response to a patent suit against linux. (This is the same sort of collaboration that I'd like to see in arena of edupatents.)
So, all in all, I don't think this particular patent threat is one that we should be immediately concerned with.