Advised = if you don't do it, you'll go to jail. That's what it means in this case.
This guy may or may not be the Linode hacker, but he sure as hell knows who the Linode hacker is.
Most likely it means that they will not be protected by the safe harbour provisions of the AML/CTF Act if they do not perform appropriate ongoing customer due diligence in relation to this customer - that requires them to take satisfactory measures to establish the true identity of the customer and the destination of funds according to the AML/CTF Rules Instrument which derives its authority from the Act.