Noone here can tell you. I can only tell you the situation around our samples:
The exact license the samples are offered under is GPL2. GPL2 is a source license.
You can do whatever you want with derivative works, just don't relicense anything from lmms samples library as your own!
To be clear, the exact license the samples are offered under currently is GPL2. Since GPL2 is a source license, that doesn't really help when using artwork or binary files.
As of right now, you can do whatever you want with derivative works, just don't relicense anything from our samples library as your own until we rebuild them in a true CC0 fashion.
-Note, bundled project files aren't C00 cleared either.
So thats the situation with the samples that comes with LMMS!
How to cope with random stuff you get from the internet, is not possible to answer, only the owner can.
Besides that, since you are new in Forum
Welcome hpik3049!
Here are all important links:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
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