Advocated the destruction of Israel (big surprise, huh?)
Which tells me two things: a) we've been watching them for a good long time, and thus we know who they're talking to; and b) the benefits of watching them no longer outweigh the benefits of shutting them down.
Item b) says that we're probably going to hear about more arrests, and item a) says who will be arrested.
I think it's not an accident that these arrests are taking place so soon after last week's terrorist warnings.