Track pad acting on its own

I saw a discussion from 2010 on this same topic but saw no resolution. This is the first time I'm posting to this community so I apologize if this is not the correct protocol. My trackpad is acting as if it has a mind of its own. My hand could not even be on it and it will move around on the screen, click on things, right click and add new folders to my desktop. While I'm working and try to use it, it becomes difficult to control and direct to where I want...it may hop to a completely different location or it will clear off the open apps swiping them to the side, or the view will automatically zoom in. It will also start highlighting words and begin taking me to definitions of them.

I took this to the Genuises at Apple. There they checked to see if liquid had gotten into the trackpad which it had not, they cleaned the surfaces with rubbing alcohol which seemed to help temporarily and I was told that I would need a new trackpad. However, it doesn't happen consistently. The weather here is hot and humid and that seems to be aggravating it. By the comments from the other postings this seems to be a consistent problem so I'm not sure why Apple would fix it for free (my laptop is a couple years old so out of warranty).

I'm also wondering if it's really a trackpad issue and not a virus or something else going on. I did find something online about something similar happening to someone using a mouse. The expert at just answer.mac offered some initial rememedies that included reseting the PRAM, trying a SAFE boot which performs several clean up procedures, and repairing the disk permissions on the hard drive. All of which I did and it seemed to help some, but still having the problem.

Would love it if someone has found a resolution or knows something else I could try. I'm leery of spending money to replace the trackpad if that's not actually the culprit.

Thanks!