My Mac is hacked! Help!
I purchased my MacBook Pro back in 2010 and I have never really had any problems with it before. Lately, I have been having incessant problems. It runs slow, my user accounts for Netflix or the iTunes store, AppStore or iCloud will log me out and will ask me to keep logging in, even though I am not by any means signing myself out. The mouse has taken to moving on it's own and making seemingly correct moves, a "Guest User" had popped up when I had not allowed it, and Find my Mac was already on for quite some time without the guest user popping up. I got frustrated and spoke to two separate Apple Support customer service reps via phone/remote in to my computer and looking around. One told me I was okay and that nothing looked out of sort, the other had me download something to get adware off my computer.
Finally, today I was incredibly frustrated and took my computer into the Apple store and they had me replace the hard drive and update to El Capitan 10.11.2, the memory is 4GB. I was hoping this would fix my problem. When I got home I plugged in my external hard drive to my computer to set it up again - my computer is still running slow, my mouse is still moving on it's own and I have been redirected to a certain website a couple times even after searching google using different phrases. I am beside myself, I do not know what to do but I do know something is wrong with my Mac yet I don't know how to fix it. Has anyone else had similar problems? If so, what did you do to fix it? What should I look for etc - any advice or knowledge would be really helpful!
MacBook Pro (13-inch Mid 2010), OS X El Capitan (10.11.2)