If they had been cross-pollinated (and nobody proved otherwise) the seeds had been his all the time. If you'd do DNA sequencing of such seeds you'd see a different DNA from the Monsanto seeds. But Monsanto claimed that as soon as the seeds produce plant resistant to their herbicide he has no right to use his own seeds.

The software analogy were, the computer virus infests your document files because you surf the same sites as your neighbors who pay "Monsanto protection." The infected files contained only the text you wrote, after running the Monsanto scanner only the infected files remain on your disk, all others are deleted. You can't preserve, copy or edit the infected files anymore because Monsanto, which produced the virus, has a copyright on avoiding Monsanto virus scanner, so as soon as the files aren't deleted by the Monsanto scanner you can't keep your own files.