One day some years ago, a user at my workplace, a large computer company, called saying his mouse had a virus. Naturally, I didn't believe him, so I went to take a look. Sure enough, his hard disk had been formatted. After doing a reinstall and restoring his documents from the backup, we confirmed that there were no errors and went on our merry way.
The next week, he reported that he had the same issue, and we found his hard drive had once again been formatted. We decided it might be a BIOS or unallocated space-resident virus, and decommissioned the machine to be sent to our forensics team, who would figure out what exactly was wrong with it. We gave him a new workstation with the same peripherals, still not suspecting the mouse.
The week after, that computer had also been formatted. Meanwhile, the forensics team had found nothing wrong with the first computer and released it back into service. We started to worry that maybe a virus had somehow copied itself to the ROM chip of the mouse, which is theoretically possible. Of course, we were overthinking it. As it turned out, the user had been complaining of random mouse movements, and had brought a Windows install disk from home and formatted his hard drive with it, somehow thinking it would remove the 'virus', which he himself thought resided in the mouse.
Long story short, he got fired and his department got mousepads.