Unless this malware wants to hide a lot of data on the drive this way, the same problem applies. For a long time hard disks have had spare blocks for invisible

Unless this malware wants to hide a lot of data on the drive this way, the same problem applies. For a long time hard disks have had spare blocks for invisible replacement it that's possible. Not to mention addressing yield in magnetic platters, you can save a lot of money by having the drive map and not use just plain bad sectors (in the bad old days they came with a printout of the bad sectors). And of course once you compromise the boot process, it's game over. Even for someone like me who uses drives as "small" as 146 "GB" for one of my system, a lot more than a few megabytes, probably more than a GiB would have to be stolen before I'd notice (well, those disks are underprovisened with LVM, but, really, can you even buy a drive with less than 100 GiB today? Not as of a few years ago, as I recall).