I grabbed KNOPPIX_V5.1.1DVD-2007-01-04-EN.iso from kernel.org, but my download appeared corrupt (MD5 hash mismatch). At first I thought the problem was in my end, so I re-downloaded it, this time from a different mirror. However, my new download also don't have a matching MD5 hash. It could just be confirmation bias, but my memory's telling me that the two incorrect hashes are the same, which implies that the file hosted on kernel.org is corrupt. As it is one of the master sites, it would explain why the mirror's also hosting the same file.

Could someone humor me and double check if they get the same results I did?

3735df5c816890d4637196493b1ded76 (INCORRECT)
e967af32cc5b9e7a91825877b65555a8 (CORRECT)