Ah. Well if you're wondering what could corrupt USB's there's many things.
Here's one thing, "One of the most frequent reasons for USB flash drive data loss is removing the media from the computer or other device incorrectly. The most common result from doing so is logical file system damage. Typically, in this situation your drive is not actually damaged even though your data is lost. But in some rare cases, the unsafe removal can also damage cells, which hold internal flash drive information, and cannot be accessed or repaired by operating systems. To extract information after this kind of failure you need help from a data recovery services professional. For this reason, it is very important to safely remove the device from the system and never unplug a USB flash drive while it is reading or writing information."
That whole paragraph is very true, although I never safely remove my usb's, I don't bother sometimes, I guess I'm lucky.