How to enforce GPL if the copyright holder doesn&#39;t have access to the source code of violating software? I'd like to publish a C library project that I have written on GitHub and license it under GPL, so I am doing some research on open source licenses and some confusion comes to mind. Let's say Evil Corps uses and modifies my code in a commercial software without disclosing their source. I have come across their software, and realized that one feature it has is very similar to what my library does. Upon my inquiry, they deny that they have used my code but also refuse to show me their source. How would I have to proceed in order to enforce the GPL? How is it done in the past to prove that the GPL is violated?
If an infringement suit is filed, the plaintiff(s) would have rights of discovery. They could subpoena the source code in such a case for comparison. They could take the depositions of EvilCorp's developers and ask them about the libraries that they used. There might well be other ways to achieve the same effect.
If you're in the U.S., then section 117 of the Copyright Act is likely what you're looking for. The U.S. Copyright Office says: Under section 117, you or someone you authorize may make a copy of an original computer program if: the new copy is being made for archival (i.e., backup) purposes only; you are the legal owner of the copy; and any copy made for archival purposes is either destroyed, or transferred with the original copy, once the original copy is sold, given away, or otherwise transferred. Based on the information you provided, it sounds like you meet all three of these criteria. They also note that your particular software's license agreement might include special conditions that affect your right to make a backup copy. Such a warning would only make sense if it was legally possible for the software distributor to make such a limitation, so I'm afraid the direct answer to your main question is "yes". It's definitely not the norm - at least in my experiences - but it is a possibility so you'll need to consult your program's license agreement. There's also a possibility that the company misunderstood you and was thinking that you were running a backup server (in the sense of a redundant infrastructure) and not making an offline backup of your entire server. It's quite normal to require an additional license for the former case.
Ideas (methods of playing, game mechanics, strategy, goals) cannot be protected by copyright. But any part of a creative work can. So, no copying of drawings, patterns, images, sounds, or the element. I suppose copying the software code is not an issue here, but it can, obviously, also not be copied. And nothing in your game can look like someone's else trademark.
In general, unless the license contains a clause which allows it to be modified at a later date through some defined means (publication, revocation of existing license etc) then you are free to continue to use the existing version of the software under the original license terms. So make sure you pin your versions! Look out for clauses such as exists in the GPL which allow the recipient of the distributed binary or code to choose what version of the GPL to apply if the original author does not state (GPLv2 Clause 9) as they then allow recipients to bind you, the distributor, to versions you might not agree with (eg the switch to GPLv3 with its patents clauses).
Content posted to the web is usually openly accessible to all (unless protected by a password, paywall, or similar restriction). But that does not mean it is freely copyable by all. Such content is protected by copyright in just the same way as if it had been published in a book of essays by various contributors. Unless the copyright holders (who are likely to be the original authors, but might not be) give permission, or an exception to copyright applies, copying such content would be clear and obvious copyright infringement, and any copyright holder could sue for damages. Permission could be given by publishing the content under a permissive license, such as a CC-BY-SA license, or any of many other available permissive licenses. Or a would-be reuser could find the copyright holders and ask for permission. If the holder cannot be found or identified, or does not respond, then no permission has been granted. In the US the main exception to copyright is fair use. See this answer and other threads with the fair-use tag here for more on fair use. Since the question seems to contemplate using the whole of the posted content, since it might well damage any potential market for that content, and since the use does not seem to be &quot;transformative&quot;, nor used for criticism or comment, a finding of fair use for this situation seems unlikely. But Fair use findings are very much fact-driven, and the exact facts do matter. Thus I cannot be at all sure whether a court would find this toi be fair use or not. In other countries there are a variety of exceptions to copyright, and I have not come close to reviewing them all. But none of the ones I know of seem to apply to the situation described in the question. Many are narrower than the US concept of fair use. I fear that without permission, copying this content would be infringement. However, it would not be infringement to create a site that includes a link to the existing content, and a summary or description of that content, along with new content, including comments on the old, with brief quotes to indicate what is being commented on.
You are framing it wrong. It is not that "they have put a barrier" to public domain information, it is that they have added an additional source of that information. The new source has a barrier, yes, but that does not prevent you from accessing the same information elsewhere. If you own a copy of some public domain data, you are not allowed to prevent other users from accessing other copies (by claiming copyright infringement or the like); you cannot even prevent people from doing copies from the copies you did provide them. But you are not forced to allow other users to access your copy. Consider the logical conclusion if that were the law. The moment that you downloaded some public domain file into your computer, you would be forced to give access to your hard disk from the internet, isn't it? Would you need to leave your home door open if you happened to have a printed copy of the text there? Of course, there is a need to discriminate between "public domain" (without licence) and "not public domain but open licence" (BSD, CC, GPL, etc.). In the later case the licence could be tailored so that the work could appear in archive.org but that it would be illegal to provide it with the business model of Academia.edu1. But that would be possible only for works not in the public domain. 1 To be decided by a judge on the basis of the wording of the licence and jurisdiction.
To use an API over a network connection (as opposed to, e.g., the Windows API), a user communicates a request to the API host, or server, and awaits a response. The host of the remote API can refuse to serve requests from users for probably any reason. Such services often require users to accept a license as a condition of using the service, and they may charge a fee as a condition of the license. A license to use a service is obviously not necessarily bound to a license for the use of its source code, just as the ability to reach the service is not dependent on the ability to see (let alone use) the code in any format, whether it be the source code or some compiled form of the code. In essence, source licenses and service licenses have different primary goals, at least inasmuch as the source license seeks to restrict someone who has actual physical access to compiled code, and possibly source code. Service licenses do not have that concern, though I have seen service licenses that also prohibit decompiling. This is probably the result of a CYA attitude among lawyers: the language is already in the standard software license text, and it doesn't hurt anything to leave it in, and it could help if a service user somehow managed to download the program code.
Am I correct to infer that content/data created by a US city have an open license (public domain if created by US city employees or open license if created by a contractor)? No. For example, Larimer County, Colorado created election administration software in-house rather than using an outside contractor to do so, and it would be lawful for it to license that software to other governments in a manner that helps recover its development costs. There is an issue over whether a city or state can copyright its municipal ordinances or statutes or regulations in a legally enforceable way when people have a legal duty to comply with them. Some courts have held that state statutes that are binding upon people can't be protected in that manner. Efforts of the West Corporation to protect its page numbering system that was widely used by courts to refer to public domain case opinions were mostly invalidated in litigation. An open question is that most municipal governments incorporate by reference in their ordinances Uniform Building Codes that are subject to private copyrights and are not terribly cheap to obtain copies of. Yet, every person doing construction work is bound to follow the enacted ordinance including the parts incorporated by reference.