Bets on who is the next?

I wouldn't be surprised if it was all of them, but perhaps Bestmixer had particularly gaping holes in how they operated.
If it were me I'd shut up shop. Or at the very least go camping in the woods and see if there are any actual charges brought from this. I can't see any mention of anyone being charged for anything yet.
My guess:
Either Chipmixer was created with this scenario in mind -- "bulletproof" so to speak (hence why they haven't been taken down yet,
(because lets be real, Chipmixer is way bigger than Bestmixer.io)
Which means they're probably chilling somewhere in the Seychelles, or some other country where they can't just raid their servers as they did with Bestmixer.
If they're not, i wouldn't be surprised if they're going to close their doors sooner rather than later. I know i probably would too. (Even if what you're doing isn't illegal. These "Shoot first ask questions later" agencies are at some point not worth messing around with anymore..)
Or.. perhaps Chipmixer has already fallen..
