Whether they have wifi on ship or not isn’t the issue. Sometimes, when a ship goes into an operation, they will turn off all signals except passive or directed signals so that they can’t easily be detected. Having a communications signal that isn’t under the control of the ship’s officers is a huge security risk during operations.
Someone is going to be court martialed over this.
I don’t know Korea’s laws but this would likely be illegal in the US, too. It depends on whether it could be proven that you knew that the stocks were issued in error. And even if it wasn’t a criminal act, the company would be within their rights to recover the mistakenly issued stocks.