Piracy is an issue that almost every creator has to deal with nowadays. But for awhile some films were only available via piracy. Take, for instance, the Evil Dead.
You might not have seen this movie or its sequel, but odds are you've seen the third one - Army of Darkness. Evil Dead is where Bruce Campbell's Ash first appeared, battling demons, killer trees, large ghosts, goblins, and his own arm.
However, for a long time, you couldn't actually buy a copy of his film in the UK. There, Evil Dead (and a ton of other horror flicks, deemed video nasties) were banned, and the only way anyone could get a copy of it was by passing the VHS tapes that they owned, copying them, and passing them on.
The large fanbase the series has, that led to dozens of videogames, and a successful musical, reboot, and television series, all of them came more or less directly from the VHS tapes passed around, illegally.