When was the last time that you updated Windows ?
The reason I ask is that it creates the windows.old folder (which is pretty large) so you can roll back to the earlier version. Microsoft Windows is meant to remove this after about a month if you haven't experienced any problems.
If it is well over a month ago that you did this windows update then this might not be a good idea to use to rollback, etc.
There is a possibility because of the contents of this folder (especially what was in the recycle bin, as that is what the alert appears to be on) it might be considered suspicious.