a ghost on my computer

For a few days in a row I would sit down at my computer to find that my mouse was moving and openeing up window boxes and then closing them. My dos opened a few times and then typing was going on. It really scared me, until I realized that it was no ghost. I was even more freaked out to learn it was some jerk that hacked into my computer over and over again!!!! I changed my windows password but it did not stop him.
I finally opened up a word doc and said “LEAVE ME ALONE” then I never saw him on my computer again.
Does this happen often????