Majordomo spam problem

I've been a LONG time user/admin of majordomo, and I've recently
experienced something I'm not sure what to do about or how to
combat.

I'm using majordomo 1.94.5, and sendmail 8.13.4, somehow evil spammers
used my majordomo mail alias to relay spam through my sendmail server.
It was a mess, I had to clean out my domain/ip from some blackhole
lists.

I picked up on it because I got quite a few majordomo abort messages.
I've been trying to dissect how they used it exactly, unfortunately,
I don't have my sendmail logs for that time period anymore.

I was able to stop it by commenting my majordomo mail alias out of
my aliases file. I was wondering if any here has seen anything like
this, and if so, how I may prevent the problem in the future.

Thanks!
-Mike

-- 
Michael Wilkinson
Game Designer              There are 10 kinds of people in this world,
Tower Ravens LLC           those who understand binary and those who don't.