I am facing the following dilemma at the moment. I am using code from a scientific paper in a commercial project. So basically I copied and pasted the code from the paper's pdf into my code editor and use it in my own code. The code in the paper does not have any copy restrictions or license(like the GPL) so I thought I would be ok using it in a commercial project.

However, I have seen several gpl licensed open source projects that use the exact same code from the paper to the point of having the same variable names like in the paper. So what happened here is that a gpl license was put on a third parties non gpl'ed code.

Are these open source projects in violation of the gpl or would I be in violation of the gpl because I use code which has been gpl'ed? My common sense tells me it is not allowed to gpl somebody elses non-gpl'ed (like in this case from the paper) code but I though I would ask anyway.