Hi Physikal,
If you could clear up what they are trying to brute force I may be able to help more.
You can always ban their IP address via the console (on the servers or Endian) using:
iptables -A INPUT -s <IP> -j DROP
If you mean SSH brute force attempts, I found that
fail2ban made a massive difference in stopping these kinda of attack.
I suppose other methods may be to just block the ports (if you can), or use Snort to sniff the packets.
Gyp