Two file-sharing companies may account for between 40 to 60 per cent of all internet traffic.

A report by networking company Sandvine, titled The Effects of P2P on Service Provider Networks, argues that the full impact of peer-to-peer (P2P) systems on the internet has never been properly assessed because it has not been measured properly.

Companies tend to calculate P2P traffic by adding up the size of the MP3 files being swapped. But the actual amount of traffic is much higher.

P2P networks have to find and then connect to four or more other computers directly, send out repeated messages to all of them, and send out and process search requests.

They then have to field connection requests from other computers, offer up search results of shared folders, and generate other computer communication that is best described as 'network chatter'.

The traffic increases geometrically for those who have programmed their software to act as a 'supernode'.

By testing open ports and writing some network mapping software, Sandvine was able to survey some 16,000 residential subscribers on several internet service providers.

It found that 15 to 30 per cent of them were using Kazaa or Gnutella clients at one time or another. The resulting traffic was huge, the report said.

The report said the fastest way to eat up bandwidth is to keep running a P2P file-sharing program.