It looks like there is a problem with our ISP in Kahnawake, which explains why other sites are affected too.
We're working on resolving the problem. If it lasts for a significant period of time, it's likely that tournaments will be rolled back according to our Tournaments Cancellation Policy:
www.pokerstars.com/poker/tournaments/rules
I will post further updates here as we have them. Please don't email support - we don't have access to the email system either.
Alex S
PokerStars Support and Game Security