A US student is being sued for showing how to get around anti-piracy technology on a new music CD. Princeton graduate John Halderman published a paper online showing how to defeat the copy-protection software by pressing a single computer key.

This has angered the company behind the software, SunnComm Technologies, which is now planning to sue him.

It is just one of the firms working on ways to make it harder to copy and trade music over the internet.

Mr Halderman found that SunnComm's MediaMax CD-3 software could be bypassed by simply holding down the shift key on a Windows PC when a copy-protected CD was inserted into a disc drive.

This temporarily disables the autorun function on Windows, stopping a anti-piracy program from installing itself on the computer.

In a statement, SunnComm said Mr Halderman had violated criminal provisions of the Digital Millennium Copyright Act, (DMCA), by revealing the secrets of the anti-piracy measures.

"SunnComm believes that by making erroneous assumptions in putting together his critical review of the MediaMax CD-3 technology, Halderman came to false conclusions concerning the robustness and efficacy of SunnComm's MediaMax technology," said the firm.

It said the company had lost more than $10 million of its market value since the report had appeared on the web.