Are they filming Oceans 52 ?
Since the FBI was called and MGM Resorts has reported the issue stems from a Cyber Security Issue.
Calling the FBI indicates to me this was not an ordinary hack, this must be much more serious.
The question is what the hackers are trying to accomplish. Was this a case of hacking the network in order to immediately steal something or was it designed to test a theory or install something that continues to operate after the network is back up and running.