In the States, Mass-BitTorrent lawsuits have been “dragging on for more than two years” and involve more than a quarter million potential illegal downloaders. The copyright owners who start these cases generally provide just an IP-address as evidence of the infringement and as the identity of the ‘John Doe’ infringer. The court is then asked to grant a subpoena, allowing the claimant to require an Internet Service Provider for the personal details of the alleged offenders. Judge Brown is of the opinion this is a “waste of judicial resources” and that the argument that IP-addresses can identify the alleged infringers is very weak with Judge Brown saying
“The assumption that the person who pays for Internet access at a given location is the same individual who allegedly downloaded a single sexually explicit film is tenuous, and one that has grown more so over time”adding
“An IP address provides only the location at which one of any number of computer devices may be deployed, much like a telephone number can be used for any number of telephones …. Thus, it is no more likely that the subscriber to an IP address carried out a particular computer function – here the purported illegal downloading of a single pornographic film – than to say an individual who pays the telephone bill made a specific telephone call”.Judge Brown went to explain that in his opinion having an IP-address as evidence of an infringer is even weaker than a telephone number, as the majority of US homes now have a wireless network - meaning that many people, including complete strangers if one has an open network, can use the same IP-address simultaneously.
This latter point was tested by the courts in Germany where the German Supreme Court (BGH) indicated that a subscriber who left their wi-fi open without password protection was potentially liable for others' infringing activities but only in as much as the subscriber could be enjoined to an action and forced to take necessary precautions - they would not be liable for damages (financial penalties) for another's infringement.
http://torrentfreak.com/judge-an-ip-address-doesnt-identify-a-person-120503/ and http://www.scribd.com/doc/92229567/Judge-Gary-Brown-IP-Address-Ruling and an opinion on copyright ‘trolls’ here http://slworona.wordpress.com/tag/judge-gary-r-brown/ and for the German position see here http://ipkitten.blogspot.co.uk/2010/05/germany-liability-for-unsecured-private.html