The site currently redirects to UGNazi.com, a site which boasts an animated version of Adolf Hitler and a short message claiming responsibility.
In recent weeks, ZUFFA has made no secret of their support for the "Stop Online Piracy Act" (SOPA), and UFC executive VP Lawrence Epstein was quoted today in an article done by the Las Vegas Review Journal (found here defending the promotion's support of the controversial act.
At this time there has been no response by the UFC, and the website remains down.