Are Linux boxes vulnerable to be used by botnets?

[Matt Graham]

After a long battle with technology, Erich Newell wrote:
[ botnets, ssh brute force attacks, etcetera ]
> I recommend Single Packet Authentication or Port Knocking for use in
> conjunction with your SSH service.

Port knocking is really useful, but you need to have something on the remote 
client that can send the knock sequences--knock or netcat or even telnet.  
This may or may not be easy, depending on what the remote client is.  So I 
have my sshd listening on 22 and a non-standard port.  22's blocked off with 
iptables/knockd.  The non-standard port is not.  I haven't seen any 
brute-force ssh attacks in the last 3 weeks according to the logs.

-- 
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Matt G|There is no Darkness in Eternity/But only Light too dim for us to see