A New York Judge has decided that just because Big Content has a "pirate's" IP address it is not enough to charge them with anything.
So far Big Content has favoured mass lawsuits as one of its weapons of choice against file-sharing and to do that it uses IP addresses to identify infringers.
New York Judge Gary Brown has decided, however, these cases tend to operate with the pinpoint accuracy of a North Korean ICBM.
He has ruled that IP addresses are insufficient evidence to identify pirates.
Brown has decided that the person who has the misfortune of having their name attached to the IP address in question isn't necessarily the one who was doing the pirating.
In some cases the RIAA's own IPs have been caught infringing - with Big Content claiming that someone else was using their Ips.
According to Torrent Freak, Judge Gary Brown makes it clear legally why IP addresses are not sufficient evidence to prosecute pirates.
He said that in the past a single, wired access point was registered to a single person and could only be used by one person at any given time.
Now wireless routers stuff up the logic that an IP address could be a person. Since 61 percent of US homes now have wireless access it is possible that a single IP address usually supports multiple computer devices which could be operated by different individuals.
Neighbours or passersby could access the internet using the IP address assigned to a particular subscriber and download a plaintiff's film.
It sounds obvious but so far it has avoided being presented as a serious argument in any court case.
But the ruling will mean that Big Content will have to come up with a lot more proof of who the pirate is, rather than an IP address.