Story : http://arstechnica.com/tech-policy/news/2011/02/reverse-class-action-its-the-lat
Imagine yourself as a lawyer who would like nothing better than to sue a few thousand people for some of the raunchiest pornography ever inflicted upon the world. You face a problem: when you sue individuals in federal court, where copyright suits are brought, you have to file suit in whichever District Court the defendant resides in. Who has the time and money to bring cases all over the country?
So you try your luck anyway, only to have federal judges smack you down and force the dismissal of most of your cases on "personal jurisdiction" grounds. This stings, and you retreat to your lair.
Then a brilliant thought strikes: there's one kind of case in which people from all over the US can be charged in a single District Court. It's called a "class action," and it's generally used when a large group of people sue a company. But flip it around - one company sues a large group of people - and you may have solved the "personal jurisdiction" issue at a single stroke!"
And hey, while you're at it, why limit yourself to suing over just one film at a time? Why not just define the class as "anyone who has stolen any of my client's movies on BitTorrent" and sue all sorts of people over all sorts of movies?