It was money laundering and fraud that the DOJ shut down those sites.I'm not sure the order is correct. Those sites were Ponzi schemes but I think the reason they were shut down was due to taxes. It was discovered after they were shut down that they were Ponzi schemes because the sites couldn't pay their customers their money.
It was just funny because it occurred on tax day in 2011.
Good article on it.
A Closer Look at Online Poker's Black Friday
I had 2,500 dollars frozen in PokerStars for 2 years because of this. Thankfully it wasn't a huge part of my bankroll like it was for others.
I have an ignition account but don't like that site. I wish online poker was legal again. Grinding $ 1- $2 games was fun.