On April 15, 2011, the U.S. Attorney's Office for the Southern District of New York seized and shut down Pokerstars and several of its competitors' sites, alleging that the sites were violating federal bank fraud and money laundering laws.
But here is the quick answer. PokerStars is not rigged. It just appears that way sometimes due to the incredible speed of online poker. Because online poker sites like PokerStars typically deal hands 3 times faster than a live poker game, you should expect 3 times as many bad beats.