Z:gnu-www-ja-assigning-copyright--f32910-Since you got the program unde/en

Since you got the program under the GPL, when you distribute a modified version you have to license it under the GPL. If the company receives a copy, it will be able to use those changes under the GPL; it won't be allowed to include your changes in that program and sell exceptions for it. It also won't be able to release purely proprietary versions containing your code. If this is the outcome you want, you get it by default. However, if the company intends to sell exceptions, it will probably decide not to use your changes.