Export Rescue: USB Check
Step 1
Check the USB on the computer
The moment the drive mounts, the computer may offer to format or initialise it. Say NO. On a Mac the button is labelled "Initialize…" and it opens Disk Utility, one step from wiping the drive. Nothing is lost yet. Choose Ignore or Eject, then answer below.
Plug the USB into the computer. What happens?
You follow these steps at your own risk. Full disclaimer.