US parents could face full liability if their children are discovered to have illegally downloaded copyrighted MP3 files and stored them on home computers, legal experts have warned.

Parents will be held responsible for any consequences arising from their children's downloading of copyrighted music if they know about it and permit it, or if they have the opportunity to prevent it and fail to do so, according to lawyers at US law firm Bricker & Eckler.

The lawyers explained that the Recording Industry Association of America's move to identify individuals who have allegedly download and shared copyrighted music by issuing subpoenas to ISPs, means that the issue of responsibility and liability has gone from "a slow simmer to a brisk boil".

Although the law firm said that US law does not require parents constantly to monitor their children's internet activity, it warned: "The deciding liability factor will be whether a child's behaviour was sufficient to alert a reasonable parent that he or she was downloading music files illegally.

"Parents who are aware of MP3 files on their computers should find out if their children paid to download those files."

In addition to civil liability, Bricker & Eckler indicated that file-sharers may now face criminal misdemeanour or felony convictions under the federal No Electronic Theft Act.

The legislation punishes individuals who wilfully copy, distribute and traffic in copyrighted works on the internet.

The reproduction or distribution of 10 or more copies of copyrighted works with a total retail value of at least $2,500 constitutes a felony, with a maximum jail sentence of three years and a fine of $250,000.

The reproduction or distribution of one or more copyrighted works with a total retail value of more than $1,000 constitutes a misdemeanour, with a maximum custodial sentence of one year and a fine of up to $100,000.

"Given the popularity of file-swapping among teenagers, parents must speak with their children about downloading music before they are forced to pay the Pied Piper," warned the Bricker & Eckler lawyers.