Serial downloaders of illegal music may not be reporting child pornography because of the misplaced fear that they will be prosecuted themselves if they do so, it has emerged.

Although the hotline service operated by the Internet Service Providers Association of Ireland (ISPAI) processed more than 2,100 reports of suspected illegal child pornography content last year, the total number of reports which it subsequently found to be "probably illegal" fell by almost a half to 284.

While this has been welcomed by both justice minister Dermot Ahern and the ISPAI, it has prompted fresh concerns that many of those engaged in spreading child pornography around the internet are becoming increasingly adept at hiding their tracks. One way in which they can do this is by using more specialised "peer-to-peer" filesharing services, which are harder for the authorities to monitor.

Peer-to-peer services are also frequently used by individuals who wish to access copyrighted material such as music or video for free.

According to Paul Durrant, general manager of the ISPAI, it is very concerned about the relatively small percentage of reports of suspected child pornography coming from users who may have inadvertently stumbled across such material on a peer-to-peer service. This can happen when they enter a search term which throws up a variety of responses, including links to potentially child pornographic material.

"I think it might be in part because of all the fuss there has been in relation to the sharing of copyrighted music online," he said. "They may be afraid that by reporting this material it could show the authorities that they are using it to download music." He added that the hotline reporting process is anonymous and confidential, and urged anyone who comes across such material to report it immediately.

"We know that when we do get reports from peer-to-peer services, it is not just a couple of images involved, often it is a whole library of horrific material," he added.

Overall, the hotline annual report released last week found that the number of reports of illegal material which it received decreased from 536 in 2008 to 284 in 2009. Of these, 274 reports related to child pornography, while six related to financial scams. Two other reports related to the promotion of violence, while one was drug-related and one promoted child grooming activities.