Lou,
  It could be an attack, but maybe not.  Could just be people
taking a net class and learning how to sub to a list, then unsub.
I get that quite often.  When I get a slew of new subs from the
same domain, then a slew of unsubs for the same domain I don't
even look at them anymore, I delete them just from the mail index.
However, sounds like you are sub by owner and they ought to pick
an open or open,confirm  list for their practice.

Douglas