removal of virus from windows backup

Can Comodo search and find virus in a windows backup that has been stored on external drive. We can see the box and tell Comodo to scan but is it really looking through the files on that backup file.

What software have you used to create the backup? If you have created a disk image, using things like Acronis or Ghost, then the only way to scan the contents of the image is to mount that image, if the software supports it. It will then behave as if it was just another disk.

If you have used the Windows built in file backup, the CIS cannot scan the content of the backup. The only way to scan is to restore to a different location and scan.