> Initially, Paint.net was released under a modified version of the MIT License, with the exclusion of the installer, text, and graphics. It was completely open-source, but because breaches of license, all resource files (such as interface text and icons) were released under a non-free Creative Commons license forbidding modification, and the installer was made closed-source. Version 3.36 was initially released as partial open-source, but Brewster later took down the source code, citing problems with plagiarism. In version 3.5, paint.net became proprietary software. Users are now prohibited from modifying it.[1]

[1]: https://en.wikipedia.org/wiki/Paint.net#History

Paint.NET was open source, but a pirate would download the code, put their name over the author’s, and click build. That’s a very clear case of copyright violation, but the author decided it wasn’t worth the effort (especially if the pirate is in another country).

https://blog.getpaint.net/2007/12/04/freeware-authors-beware...

The author blogged about it in 2009 [1]

TL;DR They used a MIT licence and other people were selling broken, rebranded cashgrab copies without changing things like the installer or crash logs being sent to the author etc

[1] https://blog.getpaint.net/2009/11/06/a-new-license-for-paint...