Copyleft troll
Someone who treats GPL violations as a revenue stream rather than as leverage to get source code released.
The concept acquired a face in Patrick McHardy, former chair of the netfilter core team. During the 2010s he sent warning letters to German companies, got them to sign undertakings with contractual penalties, and then demanded payment at the next slip. The netfilter project suspended him in 2016. After a setback in a Cologne court in 2018, things went quiet.
The response came as norms rather than law. Software Freedom Conservancy and the FSF published principles for community-oriented enforcement in 2015 – the goal is compliance, not profit – and Linux kernel developers adopted their own pledge in 2017. The same pattern shows up with photographs under older Creative Commons licenses, which lacked the cure period version 4.0 introduced.