In this situation, the best software distribution model for Chris is "proprietary."
By using a proprietary model, Chris can make the software available free of charge while retaining control over its use and redistribution rights. He can include a license that explicitly prohibits users from redistributing the software, ensuring that it remains within the intended distribution limits.
- Open-source would allow users to modify and redistribute the software, which is not what Chris desires.
- Freeware typically refers to software that is free to use but may not prevent redistribution.
- Malware is malicious software and would not be an appropriate or ethical choice.
Thus, the proprietary model is the most suitable for Chris's needs.