Bitcointalk is1 a website. Websites tend to get hacked from time to time. They run on software stacks their operators run, often without much of an understanding of the different parts and how they fit together. Ergo, they tend to be vulnerable to attack from any adversary who cares to find a whole in the stack that the site operator didn't care to know about. Some incarnations of Anonymous as well as other groups have been pointing this out for a while.
I have to say though that if I were an anthrocized 3 letter agency of the US Government that had just arrested the operator of an underground market, I'd probably want to lift the database holding messages the the underground site's users were passing back and forth in "private" messages on a related venue. After having done that what better way would there be to make it look like skiddies and not l33t NSAFBIDEAOMGWTFBBQ haxxors were the intruders than to vandalize up the site. I personally have doubt that this scenario would be the case, but the world is to weird of a place to preclude the possibility.
- probably not was, but you never know [↩]