spam sneaking into a closed list?

I found a spam message that was sent out successfully to a closed mailing list, and I
was wondering if anyone might recognize what's going on and have an answer.

A few details... According to the headers, it was sent by [email protected]
(domain.com obviously substituting for the domain name) to [email protected]. The
subject was "Majordomo results: Luxury handbags on sale now.  Buy her th". And nearly
half way into the message it says "**** Command disabled."

Sound familiar or interesting? If you're willing to bite, let me know what additional
info you need.

Thanks for your help - Jim