Big changes may be in store for the Muxtape online music discovery service. The company's Web site says the service is temporarily unavailable while it "sorts out a problem with the RIAA."

Muxtape users create customized playlists by uploading MP3s, which others can then both stream and download. The company has not paid royalties for the use, and was long considered a target for legal action.

The RIAA this morning issued the following statement: "For the past several months, we have communicated concerns to Muxtape on behalf of our members. Muxtape has not yet obtained authorization from our member companies to host or stream copies of their sound recordings."

No word yet on what changes Muxtape is making or when the service will come back on line.