When I started the law firm, a German business contacted me looking for a US law firm to represent it in its copyright lawsuits against individuals who had downloaded its client's copyrighted works through the internet. Their proposed strategy was the standard -- we have an IP address that we traced through BitTorrent using our proprietary software, now go file a copyright infringement lawsuit against the John Does' who are responsible for those IP addresses, and get a settlement. After a little deliberation, I turned down their offer.
I'm sure they thought I was a bit crazy for turning them down. But, the laws in Germany are different from the laws in the US.
In Germany, a wifi provider is responsible in the first instance for what occurs over their connection. If someone downloads (or uploads) a copyrighted work, the person responsible for that IP address would be held liable. This liability is based on the responsible person's breach of his/her duty of care (Störerhaftung). It is possible to escape liability, if the responsible person can prove that someone else committed the act. See article, article, article.
In the US, however, knowing an IP address that participated in infringing conduct is not sufficient by itself to make the responsible person liable for any such conduct. US copyright trolls know this fact. Thus, they have been using the legal system to identify the person responsible for the IP address, and then counting on that person settling to avoid any negative publicity.
A recent case highlights the chasm between German and US law. Cobbler Nevada, LLC v. Gonzales, Case No. 3:15-cv-00866 (D.D.Or. June 8, 2016). In Cobbler, the District Court Judge adopted the Magistrate Judge's finding that the person responsible for an IP address could not be held liable for direct or indirect copyright infringement and sua sponte dismissed the case. See Magistrate Judge's Findings and Recommendation; District Court Order (copies hosted on Mega.nz). The District Court Judge found that the complaint failed to show that the Defendant was the likely infringer and concluded that the Plaintiff failed to meet its burden to exclude alternative potential infringers. It shall be interesting to see whether other Courts are persuaded by this Court's reasoning, or whether this represents a high water mark.