Can I be comfortable with Linux Security
I'm relatively new to the Linux scene and I'm in the process of setting up a webserver using Apache 2 on the latest release of Ubuntu 8.10. Most of what I've learned is from using google and these forums but coming from MS windows systems and knowing all about the security vulnerabilities I'm very conscious about the system security.
My system is behind a router firewall which has been loyal for years so I'm pretty confident that any incoming traffic is dropped before it even hits my system. I've also setup a custom script for iptables from an online help page to block incoming traffic and disabled port forwarding as I don't need(I don't think I do anyway), it wasn't easy I tell you:) So I'm pretty sure that nothing can get in. However I'll need to open up port 80 to allow traffic to the webserver and this is where I'm worried.
How would I know or tell that nothing is running malicously on the system, for example a trojan or shell script or key logger. Windows firewalls like ZoneAlarm, F-Secure let you know if something from inside the system is trying to get out and you have the option to enable or disable it, AV tools look for certain patterns of code to identify malicous code and highlight it but there seems to be nothing like this on Linux, not that I've found so far.
Coming from Windows where a program tells me if something is accessing the internet or maybe contains malicous code I feel my system is open and vulnerable by not having this on the Linux system.
How do I tell, do I need I to know? I little bit confidence from experts/people who know would go a long way.