Fully compliant is a bit of a stretch. They are not registered with FINRA, nor do they hold any money transmitting licenses. They are incorporated as a limited liability company... Which anyone can do online for a couple hundred bucks. However, Poloniex has been around for a couple years now and I would not be that concerned holding funds there. Just know that it is not "fully compliant" as the user above claimed, if that affects your decision to use them or not.