BitTorrent traffic is in decline in the US for the first time, according to a new study.

The protocol, used by many pirate sites as well as legal services, allows people to download files bit by bit.

It saw its share of total internet traffic fall to 7%, a drop of 20% in the past six months. However, in Europe traffic continues to grow.

Meanwhile, other video content is riding high - with NetFlix and YouTube accounting for 50% of all net traffic.

The report, from broadband measurement firm Sandvine, shows a sharp decrease in the bandwidth taken up by BitTorrent traffic, some of which is associated with the downloading of illegal music and movies.

Ten years ago, when Sandvine began compiling its twice-yearly Global Internet Phenomena Report, BitTorrent traffic accounted for 60% of the total.

The latest figures suggest that, as well as its share falling, there could be less overall BitTorrent traffic on the network.

But in Europe, BitTorrent remains popular, with half of all uploaded traffic still attributed to the protocol.

Torrent-based peer-to-peer file sharing is on the decrease, partly because people are turning to other ways to swap material.

The use of "dark nets" such as Tor and encrypted digital lockers is growing in popularity.

These can be harder to track.

But also people are simply turning to legitimate services.

"If this trend continues I think it can most likely be explained by the increase in legal alternatives people have in the United States. In Europe and other parts of the world, it's much harder to watch recent films and TV shows on demand so unauthorised BitTorrent users continue to grow there," said Ernesto Van Der Dar, founder of news site TorrentFreak.

Mark Mulligan, an independent analyst, agrees. "We are finally at the start of having enough compelling legitimate services that the reasons for piracy begin to fade," he said.

"That doesn't mean that a hardcore of users won't continue to use these sites because they will."

Six strikes

Copyright holders in both the US and Europe have taken a tough stance on internet piracy in recent months.

In the UK about 28 sites, including many that use the BitTorrent protocol, have been blocked by ISPs following court orders from rights holders.

In the US, the government launched the US Copyright Alert in March. The system is also known as Six Strikes because it allows users six chances to stop infringing copyright.

It involves sending a series of warnings - the first two tell consumers that they have been spotted downloading illegal content and suggest alternatives sources.

The next two warnings pop up as a message on users' browsers, which people must acknowledge before they can continue.

After that the ISP will begin to throttle bandwidth or block websites.

In July, France put an end to a similar policy that threatened persistent offenders with internet bans.

The culture minister said that the penalty - fines of up to 1,500 euros ($2,000; £1,250) - was disproportionate.

Copyright holders continue to pursue piracy in all its forms on the web, and websites that publish song lyrics have become the latest target.

The US National Music Publishers' Association, an organisation set up to protect the copyright of songwriters, said that it had sent takedown notices to 50 sites that it claimed profited from advertising around lyrics "without compensating songwriters".