Don't forget to read this though everyone, please.
** What to do if I spot a program that is possibly infringing Minetest's license?If you think that a certain program is infringing on Minetest's LGPL 2.1 license, please check with the program's website to see if it is licensed under similar terms, and if the source code is being distributed. If the license seems to be proprietary, and if the developer alleges that the program is their own work, then contact celeron55. Alternatively, join the Minetest IRC channel and report it there. It doesn't matter if anyone replies or not, it will be logged and the community will check on it themselves.
***What not to do if a program is infringing Minetest's licenseEven if it is as clear as day that a certain program is using code and artwork from Minetest and is not distributing it under similar conditions, please do not attempt, or do the following:
Do not launch a witch-hunt. This is the 21st century. Please behave appropriately.
Do not attempt to crack, grief, or crash their servers.
Do not attempt to contact the infringing program's developer. Any contact made with the developer shall be after consensus with respected members of the community at large and the Core Development Team.
The above has largely only resulted in a lot of drama, mostly ending with the infringing developer gaining the upper hand and getting away with using Minetest's code while violating the license.
Please don't do it.
http://wiki.minetest.net/Licensing
Flick?... Flick who?