Look like some obvious market manipulation. I don't think it's a hacker network. They've nothing to gain for destabilizing prices. They could easily use their botnet to mine coins, steal passwords etc.
And I wonder why I still can't post in other forums.
They way I understand it they wait till MT.Gox has a high price then they sell their coins. When the price drops they attack it and cause it to go down hoping all their sell orders go through at the higher price rather than the lower price.
Something like that anyway.