I had Norton Antivirus on my laptop PC for 2 years. During that time I noticed my PC ran slowly and was subject to brief freezes and exceedingly long access times when opening files & folders as well as unusually long access times to the internet. After trying to fix the problems myself via reviewing the Start-Up processes in Task Manager and etc, I came across several reviews by folks having similar issues. The common denominator comments were related to Norton Antivirus as being a major system resource "hog", and thus slowing down overall performance.
I decided to heed the info and UNINSTALLED Norton Antivirus. Amazingly I now find that my PC is running at the speed it should be and file access and Internet use is light speeds faster than before. I now use AVAST antivirus and love the design of their product and the fact that it does not have any adverse impact upon PC performance. I realize Norton used to be a great product, but perhaps it has not enhanced basic code structure in its product to prevent these problems. Not sure.