Internet service providers determined to clamp down on file-sharing are fighting a losing battle, say analysts.
Pulling the plug on file-sharing is not so easy
Increasingly peer-to-peer (P2P) software, which allows surfers to share music and video files, is dodging the defences of internet service providers.
It is becoming technically harder and harder to win the battle against file-sharing, said Sandvine, a firm that provides equipment to manage networks.
"The range of P2P defences available to service providers has suddenly become very limited," said Marc Morin, Chief Technology Officer at Sandvine.
"Managing the way this generation of P2P application impacts the networks requires techniques that are nimble enough to facilitate easy re-engineering," he said.
All traffic to a network goes through so-called ports and in the past P2P services have been assigned to a particular port.
Now developers of file-sharing services have redesigned the applications to use random ports.
This port-hopping renders traditional blocking methods ineffective or even obsolete, said Sandvine.
Service provides are determined to do something to limit the amount of expensive bandwidth such services are eating up.
They are also under pressure from the music industry which says that the online trade in free music is undermining CD sales.
Some UK providers are clamping down on heavy users of P2P services by limiting the amount of daily downloads people can make although this has proved very unpopular.
Freeserve is writing to its customers advising them not to download unlicensed music and several providers have set up legitimate alternatives.
Analysts estimate that up to 60% of the traffic to internet providers is P2P services and it is becoming an increasingly mainstream activity for people with a fast internet connection.