(UPDATE 3) Hacker's group Anonymous called for attacks via Twitter late Thursday afternoon in retaliation for the shut down of Megaupload and the arrest of key executives. By evening on Thursday, major sites including the RIAA, MPAA, BMI, Universal Music, Warner Music Group and even the U.S. Department of Justice were experiencing major outages.
This morning, many of the sites were back online. But as of 2:20PM ET, both major label sites Warner Music Group and Universal Music Group, were still not loading. "The Site is under maintenance. Please expect it to be back shortly" read the message on http://www.universalmusic.com/.
There have been no official comments from either label group.