Unknown has altered windows system files

I had a computer that was locking up on me and I used drwatson to help trouble shoot.
I noticed many times when I boot up and run drwatson I get a message that says
Unknown has altered windows system files.
I ended up reloading the OS because thelockups got to the point of not being able to use it and this user needed it back fast.
After I reloaded it and run dr watson i get the same message sometimes.
Sometimes it tells me norton anti virus has altered files but there is no error.
Is this a cosmetic error?
Should I be concerned about it?
Right now there are no visable errors