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I am installing a Debian server which is connected directly to the Internet. Obviously I want to make it as secure as possible. I would like you guys/gals to add your ideas to secure it and what programs you use for it.

I want part of this question to cover what do you use as a firewall? Just iptables manually configured or do you use some kind of software to aid you? What's the best way? Block everything and allow only what is needed? Are there maybe good tutorials for beginners to this topic?

Do you change your SSH port? Do you use software like Fail2Ban to prevent bruteforce attacks?