[YLUG] Security problem

[chl501 at york.ac.uk]

Hi everyone,

I have a stupid question. Hope someone can give me advice.

The question is - though administrator generally do not worry about 
security of Gnu/ Linux system , Gnu/ Linux still might be infected by 
Trojan. Therefore, how can I make sure my system is safe? I have setup 
iptables. The rule is as A).

Daily activities I use only involve in programming (c/ java), surfing 
online (firefox), chatting (gaim/ skype). Seldom I would use root to 
install software, except using apt-get.

What action I need to perform (or what software to install/ document I need 
to read) in order to make sure the system is not infected?

My system is Debian sarge (testing), kernel 2.6.16, iptables 1.3.5

I appreciate any suggestion. 


A.) ========== iptables BEG Chain INPUT (policy DROP) target prot opt 
source destination ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ACCEPT all -- 
0.0.0.0/0 0.0.0.0/0 state RELATED ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state 
ESTABLISHED ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 0 ACCEPT icmp -- 
0.0.0.0/0 0.0.0.0/0 icmp type 3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp 
type 3 code 4 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 4 ACCEPT icmp -- 
0.0.0.0/0 0.0.0.0/0 icmp type 11 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp 
type 12 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 14 ACCEPT icmp -- 
0.0.0.0/0 0.0.0.0/0 icmp type 16 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp 
type 18 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
========== iptables END