In order to port forward on a Mac, you can go to the website below and download a program called Port Map. http://www.codingmonkeys.de/portmap/
All you have to do is open that program up, hit the + button at the bottom, type in '25565' in your Local Port, and leave everything else alone. Except maybe the Description. Run your server, and tada, your Port is Forwarded.
I own and operate one Minecraft server and it's fine. But outside of the Minecraft world, I've been port forwarding since 2004 for various things (remote desktop, hosting other games, etc) and nothing bad has ever happened on my network.
The only unsafe thing which COULD happen would be a DOS or DDOS attack, which is fairly unlikely.
Some little putz tried to UDP us he failed and got a permaban
Generally you're very safe with setting up a minecraft server. Doing it wrong often leads to minor hackers and griefers, but nothing computer-shattering.
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"If we put our lobster bibs on backwards and swam around in the ocean, would crabs come over to us and think we were some kind of god-king?" - towely10, 2/22/13
ImmaBoss1234 does servers inter-fear with your internet connection because after we set up a server our internet connection wasn't working? We have made a server now, so thank you to every one who helped us!