Viruses spread to different computers through pen drives.The viruses are capable enough to copy itself to whatever flash drive is attached into the infected computer’s USB drive.If you write protect your USB drives deleting/Copying files or Folders on the USB drive is not Possible.Thus virus is also prevented

Here is a freeware utility to make your USB flash drive write protected in single click.USB Write Protector is a portable application that prevents viruses getting copied to your flash drive themselves.

Download: USB WriteProtector