Usually when software is developed for a payment, the copyrights lie with the organisation paying the money, not with the developer, except when specified otherwise, which rarely happens. Many employment contracts even state that all software developed is owned by the company you work for, including software you develop in your private time. The reason for this being that you are not supposed to work (paid or unpaid) without written permission from your employer, and that there is often a thin line between what you do for your work and what not. In most cases employers don't mind you develop software in your private time and claim copyright, but there might be cases in which they might want to claim copyright, when for example, you develop some algorithm using knowledge you learned while working at your company that in someway could be profitable for your company.