Replace the current license with GPL v3

Our current license is written by us(I guess?). I doesn't cover a lot of cases. What are is the license of the modified code? Is some third party allowed to use our code for commercial purpose. Is it necessary of them to give us credit?

Even if we cover all the cases I don't think we should be writing our own license. Lawyers can always find loopholes and enforcing the license becomes pretty difficult. The suggest we should replace the current license with GPL v3. It is endorsed by FSF and I have heard of cases where FSF has fought cases to enforce the GPL. It helps to go with the herd at times.