This clock starts ticking the moment record labels present Napster with lists of songs they want banned from the song-swapping service, which has drawn more than 50 million people into a free-music frenzy.

RIAA president Hilary Rosen was quick to respond to the news. “We are gratified the District Court acted so promptly in issuing its injunction requiring Napster to remove infringing works from its system.

“We intend to provide the notifications prescribed by the Court expeditiously, and look forward to the end of Napster’s infringing activity.”

Napster did not immediately issue a statement.

At a hearing last Friday, attorneys for Napster and the music industry argued before Judge Marilyn Patel about their concerns on sharing the burden of detecting the infringing files and adapting the service to weed them out.

Music industry attorney Russell Frackman told Patel that Napster should start blocking access to songs listed on Billboard’s Top 100 singles and Top 200 albums charts, and by policing its system to keep those lists current.

Napster attorney David Boies said the burden should be on the record labels to find infringing MP3 files on Napster and then make notice of those files to the company.

Napster tried to deploy a system over the weekend to screen its system for 1 million song filenames that include various permutations and spelling of titles from Metallica and Dr. Dre, artists who have previously sued Napster and have now joined the recording industry’s suit.

Napster’s weekend plan was a pre-emptive move against Tuesday’s injunction. The new screening technology had mixed results, blocking access to some Metallica tunes, but not others.Meanwhile, users flocked to Napster for last minute downloads and also swamped alternatives services like Gnutella and Napster clones.

A program called Napigator directed hundred of thousands of music fans to servers located around the world that can be tapped into using the Napster application. On Monday, more than 96 million music files being traded by more than half a million people through computer servers located as far away as Italy, New Zealand and Russia – numbers that rivaled Napster itself even as downloads peaked this weekend.

All parties are due to meet with a mediator March 9.