Does Microsoft have a plan to sue Linux vendors for patent infringement?

Microsoft chief Steve Ballmer appeared to suggest as much in an interview with Forbes last week, saying just enough to fuel speculation, without really giving anything away - the famous strategy of sowing fear, uncertainty and doubt (FUD).

"Well, I think there are experts who claim Linux violates our intellectual property," Ballmer told Forbes' Daniel Lyons. "I'm not going to comment. But to the degree that that's the case, of course we owe it to our shareholders to have a strategy. And when there is something interesting to say, you'll be the first to hear it."

By "intellectual property", Ballmer probably means "patents", according to commentators in the open source community, since Linux is unlikely to infringe on Microsoft copyright or trademarks. However, since patents cover ideas rather than their implementations, there is no way of knowing how many patents any given software project may infringe, according to industry observers.

"Given the size of the Linux code, itÂ’s almost certain that it will violate a number of patents, and some of them, such as the ones on the FAT file system, may indeed be held by Microsoft," said Florian Mueller, a developer and lobbyist who helped defeat a European software patent directive last year.

The remarks are a progression in Microsoft's use of patents as a weapon, at least a rhetorical one, against Linux, said Mueller. In a 2004 interview, Ballmer referred to a then-recent report from an insurance group that alleged Linux violated more than 200 patents.

"Open source software does not today respect the intellectual property rights of any intellectual property holder," Ballmer said. "Some day, for all countries that are entering WTO, somebody will come and look for money to pay for the patent rights for that intellectual property." Now Microsoft is saying that it might sue Linux vendors itself, Mueller said.

Linux and other open-source software is no more susceptible to patent infringement than proprietary software, according to Stefano Maffulli, chancellor of the Italian branch of the Free Software Foundation Europe. The difference is that open-source projects don't have the funds to defend themselves against lawsuits or reach cross-licensing agreements with competitors, as companies such as IBM and Microsoft routinely do.

"The problem is that no developer can ever be sure not to infringe a patent - his software consists of hundreds or thousands of ideas, which may all be patented. How could it be possible to check? " Maffulli said.

He said he wouldn't be surprised if Microsoft did use patents to attack open-source software. "Microsoft cannot buy out Free Software, like it usually did in the past with other competitors, so we suspect that their strategy is to abuse the patent system."

In the past, Microsoft has downplayed similar remarks by Ballmer. Following the 2004 interview, Microsoft pointed out that Ballmer was referring to a report prepared by an insurance company with no connection to the software giant: "This was not a Microsoft report nor is this a Microsoft 'warning'," Microsoft said at the time.

Microsoft was not immediately able to provide comment.