-- __NO__ spam, not one, has gotten thru to the list moderation interface (the lists are hand moderated) -- Precisely 4 virus messages (castrated by the MIME stripper) have made it thru to the moderation interface. None had an active payload remaining.
Several layers of protection are available to keep spam and viruses from being distributed directly over majordomo mailing lists. That is not the problem. The problem is list members spreading viruses to other list members indirectly. Posts to my lists are informative and many members save messages which are important to them. If a member gets infected with a virus, that virus sends copies of itself to all addresses found on the infected computer, including the senders of those list messages which are saved.