Napster's file filtering system, as implemented Monday morning, is not fool proof.

By Monday, users had found ways to bypass the system. The filter, designed to halt the distribution of copyright material, was put into place at 10pm Sunday, Pacific Standard Time (Monday, 6am GMT).

The filtering software sits between the end user's computer and Napster's servers, so although a user may have one of the blocked songs on his or her hard drive, other users searching for the title cannot see it. However, as Napster has warned, one of the flaws of the system is that it can filter out only exact file names; songs with file names that have been misspelled or made up by users won't be blocked.

Filter hole Napster's search engine can track down song titles even where a name is slightly misspelled or altered, so it was possible to access some songs that were supposed to have been blocked. The Napster representative provided the names of three songs that are on the filtering list. Two of those three songs could still be accessed on Monday afternoon.

"The filtering engine has to be limited by definition, or else it would block out more songs than intended," said Malcolm Maclachlan, an electronic media analyst with International Data Corp (IDC).

Maclachlan said: "I don't think the filtering software is really that relevant. Thanks to the media coverage, every Napster user knows the name of a half dozen other sites they could try."