What is the best security application for linux?

thanks, can you please elaborate what makes it so good?

alright. I might give it a go sometime soon.

root gets alerted when someone else enters logs in as root

Do you mean NIDS (Network based Intrusion Detection System) and HIDS (Host based Intrusion Detection System)? I would disagree that iptables can secure your computer from network attacks completely. And i believe OSSEC HIDS to be a better software than apparmor, don't you agree?

I tried UCF for IP tables, guard dog and default firewall for Linux Mint. Unfortunately all of them are disappointing. The objective is to prevent the rouges from infecting your system. But all the above I mentioned provide a way to completely block or allow certain channels rather than selectively disarming the threat, like that of zonealarm. OSSEC HIDS looks strange to me, hope it does the job!

UCF and default firewall for mint are a far cry from zonealarm in terms of user friendliness. As for guard dog,it was a good firewall but not anymore. It is not supported anymore and the last version of guard dog that was released was in 2007. IPcop was another highly popular firewall application, but it too met with the same fate as guard dog. The firewalls that i would recommend others would be firewall builder and shorewall. OSSEC HIDS is an awesome tool, i think everyone should try it, another plus point is that it is supported by trendmicro, a leading antivirus company