Napster has disabled its file-transfer service while installing new song-filtering software.

Although chat and search functions continue to work normally, Napster has disabled all previous versions of its software, to comply with a US court order requiring it to prevent copyrighted material from being traded over its service. Napster 10.3, the latest version of its software, is available for download.

Napster officials would not speculate on how long it would be before users could resume song swapping: "We're working to bring it back up as soon as possible," a spokesman said on Monday. "We're not speculating on a time frame. "

Since Napster began imposing new restrictions earlier this year, the number of songs traded over its servers has dropped significantly, according to digital-music research firm, Webnoize. The firm reported last week that users had an average of only 1.5 songs available to trade on their computer, down from an average of 220 in February.

Napster has announced plans to launch a new, fee-based version of its service in the next few months. Despite Monday's problems, the company said it remains "on track" to launch the new subscription service in the third quarter.