Not Picking up viruses on real time scan

I am building a system based on Linux Mint 17 64 bit specifically to extract user data from “broken” Windows drives. If I scan a directory within the ntfs drive Comodo picks up and isolates the file containing the virus - no problem. However, when I a copy of the same directory from the ntfs volume to another location it does NOT pick up the virus. The virus is in a .txt file.

Any suggestions?

Solved. Picks it up fine if I copy into the linux filesystem but not if a copy direct to an external usb drive. Any idea why this is?