An interesting case is developing in the US which might have an effect on the ongoing effort to combat online piracy through the courts. Paramount Pictures are suing Russell Lee of Ohio over allegations he illegally made a copy of the film 'Coach Carter' available to share via the eDonkey P2P network. However, Lee denies the allegations, telling TV network News 5: "I don't even know what they're talking about. I didn't do it".
Paramount's case is not helped by the fact that when they seized the four computers in Lee's home none of them contained any record of the movie file in question. While the movie company are alleging that Lee had his computers "cleaned" to erase the evidence, it seems increasingly likely that the file was actually shared by a third party who tapped into the WiFi network Lee has in his home.
Lee's WiFi network was unsecured at the time the movie file was allegedly shared, meaning anyone could have anonymously accessed the internet via the connection. Assuming Paramount cannot produce evidence to dispute that allegation, the movie studio would have to sue Lee not securing his internet connection, which probably isn't a lawsuit they would want to pursue.
Of course if Paramount drop or lose their case with Lee it could possibly provide file sharers with a powerful new defence in P2P lawsuits - "the file sharing may have come from my internet access, but I didn't do it and I have no way of knowing who did". To overcome that defence content owners would need a clarification in the law that says owners of WiFi connections are responsible for all files that pass through that connection. But such a law would not be popular with the internet and technology firms for whom the roll out of the WiFi home is an important future revenue stream.