RE: How to tell if a Linux machine is a zombie?
> If I understand the matter correctly, a firewall can protect only
> against incoming messages, and is useless against spyware which
> "phones home" or zombie-ware which spews email spam.
Not totally correct. A firewall is only as good as the traffic that is
permitted to flow across it. If you want to block something from phoning
home then yes you can block outbound traffic as well.
Typically firewalls are as good as the person who set them up and what is
permitted to flow across the firewall.