With looking at source, you have to distinguish between copyright (the license) and possible patent status. You should indeed be careful when looking at code wi

With looking at source, you have to distinguish between copyright (the license) and possible patent status. You should indeed be careful when looking at code with an unclear license, as this opens you up to claims of copyright violations. However with patents, the situation is different (which makes them so problematic). Patent violation is solely based on whether your code violates a patent or not. Having looked at other sources or not doesn't change anything about the possible violation. This is, what makes patents so nasty.