Software patents affect a small part of the world. As a citizen of a state, where software patents are not a thing, I am personally not concerned with that. However, as a developer I am concerned with my clients, as many of them are citizens in states, where software patents are a thing.

The question is about the liability of the end user - are end users potential targets for prosecution on basis of software patents, if they use software that "infringes" on a local software patent? I do understand that if I was a citizen of such a state, I'd have legal problems with releasing such software, but the question is strictly about the end user.

Is there any difference between proprietary and open source applications?

Lastly, and I don't know if it makes a difference, but I am not talking about stealing source code, but engineering something that has been engineered over and over again, until someone happened to patent it, not necessarily and usually not the first one to think of it.

EDIT: Care to explain those anonymous downvotes? No constructive criticism? Or is it just genuinely a bad thing to be concerned with your customers?


At least in theory an end user could be sued for infringing on a patent, especially a method claim. Given the cost of a patent lawsuit, this strikes me as extremely unlikely to happen though, unless the user in question were an extremely large company, or something on that order.

Theoretically, the only difference between open-source software and proprietary software would be that availability of the source code makes it easier to prove use of a patent in open-source software. Releasing the software as open-source doesn't confer any immunity from patent law or anything like that though. Realistically, however, the chances of being sued for infringement if you're basically giving away the software in question are fairly remote. It rarely makes sense for a patent holder to spend millions of dollars on a lawsuit where they stand no chance of even recovering their cost (but no, that certainly should not be taken as legal advice that you're free to infringe on patents, or anything similar--in fact, none of this should be taken as legal advice at all).

If you can actually prove that a technique was published or publicly known and used (e.g., in a product that was offered for sale) well before the patent was applied for, the patent is probably invalid (and if proven so in court, the case would normally be dismissed with prejudice, which basically means the patent holder wouldn't be able to sue anybody else for infringement of that patent). I'd note, however, that in my experience this is much less common than most people imagine--many look at (for example) the title of a patent, and assume it lacks originality because it refers to some well-known technique, and ignore the claims where it details the precise differences between the previously known technique and what the patent really covers.

Just for example, the EFF used to have a web page talking about a (now long-since expired) patent on how to draw a cursor on screen. In an apparent attempt at scaring the unwary, they showed code they claimed infringed in the patent--despite the fact that the patent's "background of the invention" specifically cited the technique they showed as being previously known, and not covered by the patent.

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    @ddriver: I agree that you shouldn't be able to patent something that's obvious. Patent law (at least in the US) agrees. The problem is in deciding exactly what really is obvious--especially when many of the best inventions eluded many people for years or even decades, but seem almost blindingly obvious in hindsight. – Jerry Coffin Feb 10 '16 at 18:07
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    @ddriver Common sense is not subject to IP. Patents are given in exchange for public disclosure. Averages "dudes" can certainly create new and useful inventions. It's extremely rude to suggest that all patent lawyers be fired or murdered. This paper gives a good explanation of "hindsight bias" and how all things can look "obvious" after the fact. – user3851 Feb 10 '16 at 18:07
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    @ddriver: IMO, you're badly mistaken. I've written a couple of blog entries about why. See: coderscentral.blogspot.com/2012/09/…, and: coderscentral.blogspot.com/2012/10/…. – Jerry Coffin Feb 10 '16 at 18:26
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    @Dawn: Yo don't have to sue to have the patent invalidated by prior art. 35 USC 302: "Any person at any time may file a request for reexamination by the Office of any claim of a patent on the basis of any prior art cited under the provisions of section 301." – Jerry Coffin Feb 10 '16 at 18:51
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    @ddriver Invalidation happens frequently: Only 22% of ex parte re-examinations survive with all claims unchanged. Here's one example - appleinsider.com/articles/15/08/17/… – user3851 Feb 10 '16 at 18:57

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