You need to verify if the subfolder is hidden or not.
http://windows.microsoft.com/en-US/windows7/Show-hidden-files
Then perform a virus scan : http://windows.microsoft.com/en-us/Windows7/How-do-I-remove-a-computer-virus
The Microsoft Safety Scanner expires 10 days after being downloaded. During this 10 days, it will remove all the virus infected files and folders. I suggest you to create a backup of your data and then Install Microsoft Safety Scanner.