HFS+ Bit Rot
I don't know the numbers, but the probability of getting 26 corrupted at-rest files through natural causes sounds pretty much like winning the lottery twice on the same day you were struck by lightning twice<p>Checksums wouldn't have fixed this, they'd only alert the user to the fact the damage had already been done, which is exactly what the decompressor did in its own special way.<p>As another comment points out, error correcting codes are the way to handle this, and its already done in hardware, and probably too expensive to do in software in the general case