Have you heard of the media company Acacia? Probably not but actually quite a few website owners have. Many of them have received FINAL NOTICES from Acacia Media Technologies Corporation (www.acaciaresearch.com). The leading light of Acacia (Newport Beach, California) is Robert A. Berman, who claims that his company owns a handful of U.S. Patents (Patents Nos. 5,132,992; 5,235,275; 5,550,863; 6,002,720; 6,144,702) and 17 International Patents covering the transmission and receipt of audio/video content via the Internet.
If you provide access to digital audio/video content via your website without a license from Acacia, then Berman insists that you are infringing his company’s patents. So either you have to pay $1,500 per year for a license or risk being sued. It’s your choice. Some companies have paid, including porn sites. Currently Acacia is sueing (and negotiating with) the cable companies. I’m not sure whether Apple or Microsoft has received a writ yet, but if not then it’s probably coming - if Acacia continues to have success.
What does this have to do with open source? Well, simply this: Acacia is one of a number of companies that are making a good living by sitting on patents that are actually very general in their application. Individuals can register such patents, with no ability to develop associated product, wait for infringing products to appear, then get a good lawyer and go hunting. Such patents are sometimes referred to as submarine patents.
A major fear of some of the movers and shakers in the open source movement is that someone (Microsoft, perhaps, but actually anyone with a patented ax to grind) will come gunning for Linux, Apache, Tomcat et al through the courts with a fistful of patents.
Actually, there is little point in sueing the originators of open source. You have to sue someone who is using it - which means a large corporation with deep pockets rather than the average geek with empty pockets. However the effect on open source would be the same. The 'right' patent could damage an open source product badly. This is, in fact, a fear that the SCO case has brought to the surface. It is also why many large corporations like software contracts that indemnify them against such legal hunting and why the likes of HP and Novell are providing such contracts.
How big a risk is it? It’s hard to say. Nobody actually knows what patents there are that might be used against open source products and how many would stand up to a legal challenge. Patents can be challenged on the basis of prior art - i.e. someone suggested the idea in the public domain or implemented it in some way before that patent was registered. Microsoft, for example, has patented the double-click. Is there any prior art? Who knows?