Just my theory... well to start things off, a computer needs an open port to connect to the internet or whatever network/service it needs to connect. Say for instance, by default, the internet uses port 80 of your computer as its gateway. For that hacker to penetrate your system, he needs to find an open port/s, so he can do his dirty stuff but before that, he must know your IP Address. Let's say your IP Address is 192.78.200.12. He will then have to scan your computer for open ports, in this example, he found out that port 55001 was left open. So now he knows the address and at the same time, an open door(port), it's just a matter scouring your computer for anything useful to him.
This is just an overview of what is happening in an actual hacking. Anything in between are out of my scope. I can dwell into details but I opt not to because I'm still inexperienced.
With regards to pRO accounts getting hacked and such, most of the time, they are victims of people watching you type your account name and password.
