Most "backup" products, both hardware and software, don't really provide a backup.

If you attach a device to a Windows system, one that "sees" the device as a mass storage device, it will immediately allow whatever viruses, etc, live on that system to infect the medium. Within about 100 milliseconds, the device will be corrupt, and there may be no way to recover from that.

True backup hardware/software combinations don't allow the OS to read/write the device directly, so, while infected files may be saved on the device as part of a backup, they won't be able to propagate through or on that device, at least not until they're put back under the control of Windows or whatever other OS it was from which they were backed-up.

I wish USB hard drives would allow a safe backup. Unfortunately, it seems that they don't, as they immediately appear as a mass storage device to the OS, which means that they immediately have whatever viruses live on the system to which they're attached. Further, whatever such viruses/malware were present on any other system to which they have, at some time, been attached, now are on that system, too.

RE