A Finnish court has ruled that merely operating an open WiFi access point does not make you liable for copyright infringements committed on your network. From the defense attorney's press release:
This alleged copyright infringement had taken place in a specific 12-minute period in July 14 2010, a date when a summer theater play with an audience of around hundred people was held at the premises of the former school owned and resided by the lady.
The applicants were unable to provide any evidence that the connection-owner herself had been involved in the file-sharing. The court thus examined whether the mere act of providing a WiFi connection not protected with a password can be deemed to constitute a copyright-infringing act.
Crucially, the applicants also sought an injunction to prevent the defendant for committing any similar acts in the future. Had the injunction been granted, the legal status of various open WiFi providers would have turned out extremely difficult, as rights-owners would have been provided with a powerful legal weapon to shut them down in cases of similar, arguably insignificant infringements by incidental visitors and customers...
Finally, the court concluded that the WiFi owner cannot be deemed liable for the infringements actually committed by third parties.