No matter what your Linux, you need to protect it with an iptables-based firewall.
Yes! You’ve just set up your first Linux server and you’re ready to rock and roll! Right? Uh, no.
By default, your Linux box is not secure against attackers. Oh sure, it’s more secure than Windows XP, but that’s not saying much.
To really nail down your Linux system you need to follow the instructions in Linode’s Securing your Server guide.
To summarize, you must?—?first?—?turn off the services you don’t need. Of course to do that, you need to know what network services you’re running in the first place.