How do top open source projects protect their code?

its open source, everyone exposed to it protects it through advancement following environmental release...

i think you may be asking about, "hurting people for money who use code written identically in a non-changing ascii implimentation native to electronics manufactured we cant prevent from being produced, update to a universal free standard protecting all future generations exposed to it piece of dated hardware thats cheap enough to afford everyone can get one, tinker with, but others want to fuck em for cash requiring enforcement of backward idiots propoganda that human pets with badges swing off on their betters to keep the wheels of the justice system turning for."

solutions to problems dont need protecting from the people who craft them to solve problems, but for those who do so to ensure problems still exist after they are used.

Ummm - it's open source, you don't protect the code. You build on what people have done before, on the condition that others can build further on your work.