I took my Mavic to a local park for a sunset flight this afternoon and found three Phantoms already in the air. It's Christmas day, and all three were newbies (like me). But the crowded skies made me wonder...
Is my Mavic controller paired with my specific machine?
If there were other Mavics nearby, might there be a control problem?
And is it possible for someone flying a Phantom to interfere, or even take control of my Mavic?
The three I saw didn't seem to be having any problems. But I'm wondering if there's something in the OccuSync signal that pairs my specific Mavic with my controller?

Your controller is paired with your Mavic. If you buy a new controller, you have to pair it with the Mavic. There are instructions for how to do that in the instruction manual.

Your mavic is paired to your controller only, something like a preshared key in routers. Dont worry, no one can take control of your mavic.
There is a chance of interference, which will limit range, but all drones etc will try to use the least congested radio frequency automatically and they can hop to another frequency if the current one becomes "busy" mid flight. You have more to worry about them crashing into you than anything else

Just as Danny-B- mentioned, you might ran into interference at that place.
It's better to fly far away from the other drone.