This will happen, of course, if you still have not done that already on your own.
I recommend that you approach the island from the North-Eastern side.
Make it over to the shore and approach the main buildings carefully, while trying to remain unspotted.
Hack into one of the nearby cameras and start switching from one to another.
Hold down the hacking key/button to download the code.
Swim/steer away from the island and approach it from the North-Eastern side.
Take the main path towards the router.
After you get there, hide behind a cover, for safety, and hack into the router.
You will have to play the hacking minigame here.
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