When using your USB key on another computer, it may be infected by a virus, it is essential to have a program like BackUp Anywhere to store the data inside it.
BackUp Anywhere allows you to create a backup copy of your data in your USB key. The first time you use it, you must create a target destination in which all the USB files will be copied. Then, tick “Automated Mode” so that the backup will be done automatically when your key is plugged to the PC. This program also supports file synchronization.