Laura Sydell, « DIY Tractor Repair Runs Afoul Of Copyright Law », npr.com, (consulté le ) : « And the little computer screen lets him know when something is wrong. Unfortunately, Alford isn't allowed to fix it. John Deere has a digital lock on the software that runs his tractor. And it won't give him the key. [...] The company went on to say that unqualified individuals could endanger customer safety. »