Which method is frequently used to protect software?

Copyright is the primary and most frequently used legal mechanism for protecting software. Under copyright law, software source code and object code are classified as "literary works." This protection is automatic upon the creation of the software in a tangible form and grants the author exclusive rights to reproduce, distribute, and create derivative versions of the work. This legal framework is the foundation upon which both proprietary software licenses (which restrict use) and open-source licenses (which grant specific freedoms) are built. It fundamentally protects the intellectual property embodied in the code from unauthorized copying and use.

A. Trademarks: Protects brand identifiers like names and logos associated with the software, not the functional code itself.

B. GNU General Public License: This is a specific "copyleft" license that utilizes copyright law to enforce its terms, not the fundamental protection method itself.

D. Fair use: This is a legal doctrine that serves as a limitation on and exception to copyright protection, not a method of protection.

1. U.S. Copyright Office. (2021). Circular 61: Copyright Registration for Computer Programs. U.S. Government. Section: "Copyright Protection for Computer Programs." This official document states, "A computer program is a set of statements or instructions to be used directly or indirectly in a computer to bring about a certain result. A program is protected by copyright as a literary work."

2. MIT OpenCourseWare. (2018). 6.033 Computer System Engineering, Lecture 22: Intellectual Property. Massachusetts Institute of Technology. In the section on "Copyright," the lecture notes explicitly state that copyright applies to software as an "original work of authorship" and is the default protection mechanism.

3. Stanford University Libraries. (n.d.). Software & Copyright. Stanford University. Retrieved from https://fairuse.stanford.edu/overview/specific-materials/software-copyright/. The page clearly states, "Like a book or a movie, software is protected by copyright law." It further explains that copyright protects the "literal expression" of the code.

4. Lemley, M. A., & Menell, P. S. (2019). Software and Internet Law (4th ed.). Wolters Kluwer. Chapter 2, Section A ("Copyright Subject Matter") details how computer programs were established as copyrightable literary works under U.S. law, forming the basis of their legal protection.