On its face, pirating such software would seem to be illegal. But in 2015, the Librarian of Congress approved an exemption to the Digital Millennium Copyright Act for land vehicles, which includes tractors. The exemption allows modification of “computer programs that are contained in and control the functioning of a motorized land vehicle such as a personal automobile, commercial motor vehicle or mechanized agricultural vehicle … when circumvention is a necessary step undertaken by the authorized owner of the vehicle to allow the diagnosis, repair, or lawful modification of a vehicle function.”

Source: Why American Farmers Are Hacking Their Tractors With Ukrainian Firmware – Motherboard