THINK illegal downloaders of anime cartoons and the picture of a tech-savvy, pimply teenager comes to mind.

But it's no longer child's play.

The worldwide anime downloading problem is so serious that the Japanese government has sent an official request to the US government to examine its market competition policy.

In the statement, Japan asked the US to help stop the unauthorised reproduction and distribution of Japanese anime online. It was even discussed at the fourth Japan-US Trade Forum meeting in Tokyo last week.

The statement specifically mentioned the unauthorised distribution of Japanese animation and other materials on video-sharing sites and peer-to-peer (P2P) file-sharing networks.

Despite frequent requests by copyright holders in Japan for the removal of unauthorised material from video sharing sites like YouTube, the problem has not abated.

Part of the reason is the high cost and complexity of taking action against downloaders who use P2P file-sharing networks and video-sharing websites.

Just this year, local anime distributor Odex sparked a public outcry after it hired US Internet security company BayTSP to track the IP addresses of those who had used P2P networks to download its anime illegally.

With P2P file-sharing networks, users search for others who have copies of the files they want. Once these users are located, the file can be downloaded in small packets from several users at once.

Contrary to popular belief, these methods hardly guarantee anonymity.

Whenever they download anything, downloaders leave evidence of their online activities. This has spawned a game of cat-and-mouse with copyright holders.

Recently, Pirate Bay, a popular file-sharing network based in Sweden, announced improvements to its technology that would prevent tracking companies identifying its users.

A junior college student, who used to download anime regularly, said he is always 'looking for safer downloading options'.

He said: 'I prefer certain clients because they ensure our privacy.'

But 'Internet police' are fighting back.

Mr Mike Ishikawa, chief executive officer of BayTSP, said that the company constantly monitors new developments in file-sharing protocols.

On criticism that his company is infringing on the privacy of Internet users, Mr Ishikawa says these people already compromise their privacy by choosing to download illegally.

He said: 'Many downloaders don't realise that when they use file-sharing applications like eDonkey and BitTorrent, they are publicly broadcasting information about themselves, including their IP addresses.

'BayTSP only collects information that downloaders make available to everyone else on the network.'