@Werner P. Schulz
Many thanks for double-checking the .md5 and .md5.asc files of KNOPPIX V7.2.0 DVD hosted on the website of mirror.denit.net.

@utu
Thanks for the pointers. However, verifying the authenticity and integrity of whatever one has downloaded is kind of common sense. Here is an apparently less worrying server hosting old versions of KNOPPIX; ftp://ftp.sun.ac.za/pub/iso-images/knoppix-dvd/