With the flash drive disconnected, bring up your preferrede AV program. Run the update to get the latest definitions, reboot if instructed to do so. Once you are back to Windows if you had to reboot, bring up the AV program again. Now plug in the flash drive. When prompted, select the option to Open Files and Folders. When the explorer window comes up, right click on the flash drive and choose the option to scan for viruses. You should also download the free version of Malwarebytes, install it and then scan the flash drive with that as well.