It's unclear what is happening and this may be a prank. The initial reports that the FBI had seized the domain appear to be a sarcastic "down for maintenance" page on the part of Silk Road. I've yet to find a real source on the alleged arrest of

http://www.reddit.com/r/SilkRoad/comments/1nl5ne/shutdown_is...

However, there also appears to be a criminal complaint out for the founder.

http://krebsonsecurity.com/wp-content/uploads/2013/10/Ulbric...

EDIT: Seems like this is real. Reuters reports that Ross Ulbricht, the founder of Silk Road, was arrested in San Francisco. http://www.reuters.com/article/2013/10/02/us-crime-silkroad-...