With the first big batch of music now blocked from Napster's file-swapping network, the average number of songs available on the service has dropped precipitously, according to at least one research company. After the latest update of its filters Wednesday night, the average number of MP3 files publicly shared by music-swappers on the service dropped from 172 to just 71, a drop of close to 60 percent, analysts for Webnoize said Thursday. Wednesday was the deadline for Napster to block a list of 135,000 songs identified by the record industry late last week. The service is far from useless. Even many of the blocked songs, ranging from Madonna to Elvis, are still available online in some form. But many of the most popular songs and artists on the service have disappeared or are much harder to find, indicating that Napster's attempts to screen copyrighted works are in line with a recent court order. Although the amount of people on the system has remained fairly consistent, the number of files downloaded has been cut roughly in half, Webnoize analyst Matt Bailey said. Webnoize has reported that about 2.7 billion files were traded through Napster in February, shortly before the service voluntarily took the first steps to remove titles. "The first phase of the filters did have some impact," Bailey said. "But certainly not as much impact as the new filters (added) last night." Many people writing on Napster's online bulletin boards appeared resigned to the filters, but the new wave of screens drew some bitter complaints. "Napster is getting harder and harder to use," wrote "Chris275" on Wednesday night. "Is it going to stay up?...I'm sharing only 1700 out of 2800 files. Napster is going to lose a lot of people to this." The last several months of publicity have drawn people increasingly to Napster alternatives such as Gnutella, iMesh and open-source versions of Napster itself. According to Clip2 Chief Executive Kelly Truelove, whose company monitors traffic on the Gnutella file-swapping network, the average daily number of users there has jumped more than tenfold since December. Before the appeals court ruling that sealed Napster's short-term fate, only about 10,000 to 20,000 people a day used Gnutella software, compared with about 250,000 a day now, he said. Nevertheless, the progressive implementation of filters on Napster has had a smaller effect. "We haven't seen any drastic changes in the last week," Truelove said. Other file-swapping programs, such as iMesh, remain among the most popular software on Download.com, a site owned by ZDNet News parent CNET Networks. More than 400,000 copies of iMesh were downloaded in the last week, according to that site. Even if the number of songs available through Napster has dropped sharply, the blocking is still evolving on the part of Napster and the record companies. Inside the list of 135,000 songs submitted last week were many duplicates and citations that didn't comply with the terms laid out by U.S. District Judge Marilyn Hall Patel in a court order, Napster Chief Executive Hank Barry said earlier this week. For example, of approximately 95,000 songs submitted by Sony Music Group, more than 46,000 did not include a file name that had been found on Napster, a court requirement for the blocking process. As a result, the company had blocked only 59,600 total songs by the end of Wednesday, a Napster spokeswoman said. The company had no immediate comment on the figures provided by Webnoize. Earlier this week, the Recording Industry Association of America (RIAA) warned Napster not to play games with the terms of the injunction. "We are not going to debate the fine points of the order's implementation," a representative said. "We believe the court's intent is clear. Napster is required to stop infringing. Stall tactics are unacceptable." Napster is required by the court to track down and block "reasonable" variations of song and file names. On Tuesday, the company said it had hired Gracenote, which maintains a database of million of song titles, artists names and variations of these, to help track down misspellings. The music-swapping company also has employees manually finding variations of blocked songs and entering these into its database. An automated software program that will do this more efficiently is also in the works, Barry said Monday. Even with the song blocks, it is possible to find versions that have been giving alternative names that slip through the filters. Searching under "Madonna" and "Material Girl" returned no files, for example. Changing the artist's name to "Madona" returned many songs, however. A few automated programs for masking song names are still circulating around the Net. One of the most prominent, a program that turned file names into Pig Latin produced by rival file-swapping company Aimster, has been taken down at Napster's request. But other, more powerful versions of the anti-filter techniques are still available. Take me to the MP3 Special Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Napster Debate. Let the editors know what you think in the Mailroom. And read what others have said.