[nestorD]

Avoid reading the code, being inpired by it and using the same pattern (or worse, snippets) in your project (which could result in legal actions against you).

I have often heard it in the context of windows operating system developper which should be careful of not accidently introducing open-source code in the kernel if it might have a license that is not compatible with Microsoft's one.

[baby]

There’s no law against that unless you’re implementing a patented algorithm, which is dumb in any case.

[snvzz]

Alternative implementations of programs often use Clean Room reverse engineering, for a reason.

[nestorD]

What if you copy paste code that is under a viral license ?