Somebody has hacked into my MBP and taken control of it?

Someone has embedded themselves in my MBP and anytime they want they can just take control. They have complete control of the computer. I've tried wiping the drive and re-installing the OS, they still have been able to control my computer. I came up with an error one time with this string:

System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS/ARDAgent

The next step away is The Terminal. I've taken it to Apple and spoken with Tech. Support and they both said that's nothing and that couldn't have to do with the person in my MBP. I don't necessarily think that they know everything about the MBP but I could just be making a wrong assumption. Anybody know how to get them out of my MAC? I THANK ALL OF YOU IN ADVANCE FOR ANY HELP THAT YOU HAVE FOR ME, I REALLY DO APPRECIATE IT!!!!!

Hollywood