Music "mixtape" sharing site Muxtape has been pulled offline, with a notice saying it has to "sort out a problem with the RIAA." Its blog today contains the glib but equally nebulous statement, "No artists or labels have complained."

The message on Muxtape's main page predicts Muxtape will only be down "for a brief period." But the message contained in the site's Tumblr blog is slightly more foreboding, saying, "The site is not closed indefinitely."

Muxtape allowed users to upload as many as twelve MP3s to a unique URL ("username.muxtape.com") that behaved as a sort of MP3 playlist mixtape that could be "traded" with others. By making these MP3s available for streaming, Muxtape was also responsible, the Recording Industry Association of America believes, for royalties on any copyrighted material.

This is no doubt why the RIAA has intervened and why the beta of "Muxtape for Bands," a service where artists presumably upload their own music directly, is unaffected.

Interestingly, there is very little information about Muxtape for Bands prior to this week's Muxtape shutdown. Some suspect that it is a deliberate move by Justin Ouellette, Muxtape's founder, to hype the beta of a service that hasn't actually launched yet. [Personal note: As a writer for a site dedicated to beta releases who is also a musician and Muxtape user, I can say I was neither contacted about this beta nor had I heard anything about it until this shutdown announcement.]

10:50 am EDT August 20, 2008 - The RIAA yesterday issued a statement that confirmed expectations that Muxtape's closure was due to illegal music sharing and was not a beta launch stunt.

An RIAA spokesperson said the organization had tried "repeatedly" to work with Muxtape over the past several months to get the unauthorized content removed, to no avail. Judging by the amount of content hosted by the site, and its purported lack of any sort of authorization from RIAA members, the future of Muxtape as it had originally envisioned, looks bleak.