What legal protection prevents unethical duplication of a software program?

The correct choice is based on the fact that copyright law provides legal protection for original works of authorship, including software programs. Copyright prevents others from making unauthorized copies, distributing, or creating derivative works based on the original software. This protection is automatic when the software is created and fixed in a tangible medium, which means that developers do not need to register their software to have copyright protection, although registration can enhance the ability to enforce rights in court.

Trademarks, while related to brand identity and the protection of business logos and names, do not protect the actual software code or its functionality. Registration refers to the process of officially recording a copyright or trademark but does not, in itself, provide protection. The term "brand" refers more to the overall perception, marketing, and identity of a product rather than legal protections against duplication or copying of the software. Thus, copyright is the relevant law that directly addresses the unauthorized reproduction of software, making it the appropriate answer for this question.