Abstract

I have a FAT32 memory card that when inserted into a computer causes Windows to prompt to format it. The card is definitely not supposed to be blank and has a bunch of files on it.

Symptoms

Using a hex-editor/disk-viewer, I examined the card and found that several sectors/clusters have been overwritten with something that has a signature of USBC at the start of the sector. Specifically, the master boot record (and partition table) is gone (hence Windows thinking the card is blank and needing to be formatted), as are the boot sectors (they have the USBC signature and a volume label of NO NAME and partition type of FAT32).

Fortunately, it looks like both copies of the FAT are almost entirely intact (a few FAT entries at the start of a cluster here and there seem to be overwritten by USBC). The root directory is also nearly intact—I can see the volume label entry and subdirectory listings, but one sector is overwritten. (There are no more instances of USBC after the last one in the FAT2.)

Hypothesis

These observations seem to indicate some sort of virus that erases a few key filesystem structures, and then overwrites a few extra sectors here and there. Googling it seems to corroborate the idea of a virus, except that others report a file called USBC which does not apply here, and in fact, could not be possible since there is no filesystem to even see files. I cannot find any information about a virus with these symptoms, nor a removal tool. (I can't help but wonder if it is actually due to an autorun virus prevention tool.)

Question

I can likely fix the FAT corruption since they are mostly contiguous chains and maybe even the lost sector of the root directory, but does anyone know of a convenient way to restore or (re)create the MBR/partition table and boot sectors (without formatting or overwriting the data)?