You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.
I think they've revoked even Chessbase's license to use the code. So, not like a book, where if you have the physical copy you can generally read it, but more like a pirated copy of Windows or Oracle, where you owe license fees per user, per core, per day.
It's not settled law, but IMO probably not, I don't believe it's ever been tested in court.
Windows comes with a click-wrap contract that you agree to when you install it, that restricts certain things you could usually do. So it's a bit of a bad example... but I'll use it anyways.
What does (generally, not legal advice, not a lawyer) need a license is making a copy of the software, i.e. installing windows onto your computer actually makes a copy, or making a copy of the installer for your friend - makes a copy. Just booting up the machine that already has windows installed on, that's (probably) not copyright infringement even if you don't have a valid license. It might be breach of contract depending on what contracts you have agreed to though! Physically giving your friend the computer with windows already installed on it, is similarly not copyright infringement. Cloning the hard-drive so you now have two hard-drives with windows installed, that's copyright infringement.
I don't think it quite works that way: the license is really just an agreement between the user and the rights holder that they will not sue for infringement. So use without license really means "you may expect to be sued". The outcome of that suit would determine whether or not you "need to license to use code". I'm guessing there have been many cases where the copyright owners for some code sued someone for using it and won.
Using software is not one of the enumerated rights reserved to a copyright owner. Copying and distributing it are. So it's unclear whether a copyright owner has standing to sue you for using their software without a license. In the US there is conflicting caselaw, hinging on the legal status of the temporary copy made in the computer's RAM when a program is launched.
For distributing it, making copies of it, and violating contacts, definitely. For using a program already on a computer with no click through contract that you agree to to run it (or other contractual obligation), I'm not aware of any cases.
That they can sue is a non statement, you can sue for anything, but I don't believe it is obviously (or even likely) copyright infringement...
To be clear, it would be ChessBase that would be sued, not individual users. And ChessBase would be the one allegedly in violation of "distributing it, making copies of it, and violating contracts". Since their license to use Stockfish seems to be revoked, it seems like it would fall under copyright infringement at that point (although up to the courts to decide, of course).
Even if you could execute the code you somehow obtained, but for which you've somehow lost the license, for ChessBase it becomes worthless, as they can no longer distribute - whether sell or give away - anything building up on it.
Even then, IIRC CC0 is not that easy to apply to code (even CC do not recommend it for that: https://creativecommons.org/faq/#can-i-apply-a-creative-comm... ), WTFPL is entirely untested (even more so than GPL/MIT which are also not entirely tested in courts) and some regions do not recognize public domain. For example sqlite sells a license for what is public domain code partially for the reason of "You are using SQLite in a jurisdiction that does not recognize the public domain" and "You are using SQLite in a jurisdiction that does not recognize the right of authors to dedicate their work to the public domain".
Also, when it comes to code dedicated to public domain it is good to consider what wikipedia says about implied warranty: "The licensing process also allows authors, particularly software authors, the opportunity to explicitly deny any implied warranty that might give someone a basis for legal action against them." It is always good to include a clause saying that there is no warranty, implied or otherwise (unless of course you provide a warranty, which you probably should not do without restrictions on OSS code).
CC0 and WTFPL are also copyright licenses. Works available under these licenses can be used with very few restrictions (basically, as few as permitted by law), but the works are still copyrighted.
It’s simplified, but more or less accurate. CC0 is an attempt at making a public domain deed possible for jurisdictions that do not know public domain deeds like the US does. German Urheberrecht is not entirely like US copyright, some rights of the author are impossible to waive. So CC0 has a fallback for those jurisdictions, it grants a license to the fullest extend possible under the law. https://creativecommons.org/publicdomain/zero/1.0/legalcode
"Unlike the Public Domain Mark, CC0 should not be used to mark works already free of known copyright and database restrictions and in the public domain throughout the world. However, it can be used to waive copyright and database rights to the extent you may have these rights in your work under the laws of at least one jurisdiction, even if your work is free of restrictions in others. Doing so clarifies the status of your work unambiguously worldwide and facilitates reuse."
As I understand it, you can't just waive copyright on your own work - copyright is something you get automatically in most jurisdictions on the planet. Licenses like CC0 and WTFPL are operating within the copyright regime - they use the laws to make your work behave as if it was not subject to copyright - but they can't actually make your work not copyrighted.
It's like a difference between simulation and reality. CC0, WTFPL, etc. are simulating a copyright-free reality on top of the copyright system. No matter how close to perfect they get, it's still a simulation, and copyright is the underlying runtime.
It depends on jurisdiction. Some places (I think the US is one of these) do allow you to put works in the public domain, and CC0 does that where possible. The “as if” license is a fallback.
As seen in the section a sibling comment posted, the GPL terminates itself during certain conditions. So, they're either confused or trying to play lawyer a bit too hard. (IANAL)
No. Stockfish owns the copyright to their code. You can't copy stockfish code without a license from stockfish. There's no provision in the GPL for some third party to re-grant a GPL license to someone else after their license was terminated.
8. Termination.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.