Hi Justine,
If you detect the same virus again after formatting the flash drive, either the virus is being copied from the computer when you connect it or the virus was not completely removed when formatting. In some cases, adware or malwares installed in the computer without the user’s knowledge can also generate false notifications stating that the computer or a flash drive has a security threat and the user can purchase a particular software to remove it.
So to check and remove any virus or any other security threats, I would suggest you to run a complete security scan of the computer when the flash drive is connected. Make sure that the antivirus software is updated with the recent virus signatures before you run a security scan. Sometimes, some viruses can even corrupt the security software and in such cases the security software might show that there were no security threats found. In this case, I would suggest you to use the Microsoft security scanner and check for any security threats.
Note: The Microsoft Safety Scanner expires 10 days after being downloaded. The Microsoft Safety Scanner is not a replacement for using an antivirus software program that provides ongoing protection. Any data files that are infected may only be cleaned by deleting the file entirely, which means there is a potential for data loss.
When running the security scan, make sure that the flash drive is included in the locations to perform the scan. Once the security threats is completely removed from the flash drive, format the drive.
Try these steps and let us know the results. We’d be happy to help if you need any further assistance.