On May 3, Metallica delivered 13 boxes of legal documents identifying user names of people who allegedly had made Metallica songs available online and demanded that they be blocked from the MP3 music-swapping service.

As a result, the Web site has blocked the offending screen names but stated that “it is possible that users have been mistakenly implicated.”

According to an announcement on Napster.com, the company’s software “will direct all users barred as a result of Metallica’s allegations to an infringement notification page.

“That page explains the notice that Metallica has given us, explains who Metallica has stated to us it intends to block, and gives the user an opportunity to submit a counter notification if the user has been misidentified.”

Napster users who suspect they have been blocked due to misidentification can request reinstatement by submitting a counter-notification under penalty of perjury, according to the announcement.

If Metallica doesn’t pursue legal action against that user within 10 working days of being notified of the counter notification, the user may be reinstated.

“Napster has taken extraordinary steps to comply with Metallica’s demands to block hundreds of thousands of its fans from using the Napster system,” said company attorney Laurence Pulgram.

Metallica appeared nonplussed by the backlash from irate fans who continue to criticize the band’s actions on Internet message boards and chat rooms.

“This is not about Metallica versus the Internet,” Ulrich said in a statement posted on the band’s Web site. “We know that the Internet is the future in terms of spreading your music to your fans, and we’re excited about that. But we want to control how that’s done, just like we’ve always controlled what we make.”

Napster had maintained that its service should be protected by the “safe harbor” section of the Digital Millennium Copyright Act of 1998, which limits the monetary liability for Internet service providers who are sued for the actions of their users.

U.S. District Judge Marilyn Hall Patel rejected that defense May 5 and ruled that Napster was not entitled to such protection.