A spammer posted to the users list today. The archived message is here.

I marked the subscriber address as moderated on the users list. I didn't simply unsubscribe and ban the address as I could not be positive whether the subscriber may have simply had their address misused.

@mattdm suggested to one of the list users who replied on list that it should be reported here, so the spam could be removed from the list archive and the subscriber potentially blocked.