The Stockfish project, distributed under the GPLv3 license, sued ChessBase, revoking the company's GPL license to use its code. Stockfish is the strongest of the chess engines used on the chess services lichess.org and chess.com. The lawsuit is filed in connection with the inclusion of the Stockfish code in a proprietary product without opening the source code of the derivative work.
ChessBase has been known for its Fritz chess program since the 1990s. In 2019, she released the Fat Fritz engine, which is based on the neural network of the Leela Chess Zero open source engine, at one time based on the work of the AlphaZero project, open by Google. This was not a violation of any legislation, although the Leela developers were unhappy that ChessBase positioned Fat Fritz as an independent development, not recognizing the merits of the AlphaZero and LeelaZero teams.
In 2020, ChessBase released Fat Fritz 2.0, based on the Stockfish 12 engine, which has its own neural network architecture NNUE (ΖUIII, Efficiently Updatable Neural Networks). The Stockfish team, with the help of lawyers, was able to obtain a revocation of the Fat Fritz 2.0 DVD from retail chains in Germany, but, not satisfied with the result, announced the revocation of the GPL license for Stockfish from ChessBase, and filed a lawsuit.
This is not the first season of drama around the Stockfish code that commercial engines have borrowed from the GPL. For example, earlier there was an incident with the leak of the source code of the proprietary engine Houdini 6, according to which it became clear that it was based on the Stockfish code. Houdini 5 competed in the TCEC competition and made it to the Super Final of the ninth season, but was eventually beaten by Stockfish. In 2017, the next version of Houdini 6 was able to win the tenth season TCEC Super Final against Komodo. Source code leaked in 2020 exposed this unholy deception that flouts one of the cornerstones of FOSS, the GPL.
Recall that the GPL license provides for the possibility of revoking the license from the violator and terminating all the rights of the licensee granted to him by this license. In accordance with the license termination rules adopted in GPLv3, if violations were detected for the first time and eliminated within 30 days from the date of notification, the rights to the license are restored, and the license is not completely revoked (the contract remains intact). Rights are returned immediately also in case of elimination of violations, if the copyright holder has not notified the violation within 60 days. If the deadlines have expired, then the violation of the license can be interpreted as a violation of the contract, for which financial penalties can be obtained from the court.
Source: opennet.ru