I installed Avast 7.0.x 2 days ago and soon after noticed I could not rename any folders. Further, I could create new application files but could everytime I tried to save an update to a file, I was told the file was "read only" and I had to save the update as a new file.
After trying for the past 2 days to figure out what caused my file/folder problem I stumbled on this forum and decided to uninstall Avast. My system now works perfectly again.