There are lots of people who store their data on a portable Flash drive in order to always carry their private files with them. However, plugging and unplugging the device in several computers might result in malware infections that can be easily spread.
Therefore, one should always run dedicated USB scanning tools before accessing a connected USB device.
These security tools target USB-specific infections, so the scanning time will be greatly reduced compared to a standard antivirus.
These applications will typically remove the detected infection from the portable device, thus making sure the virus will not infect other computers.