Passwords are like toothbrushes - you shouldn't share them with other people, and you should get a new one every now and again.
See ChoosingPasswords for information on creating safe, random passwords.
Basic Machine Security:
- Don't use protocols such as telnet or ftp between machines on an untrusted network such as the internet - these send usernames and passwords around in clear text. Anonymous ftp is OK - you don't give away your details. Instead look into ssh(1) (Secure Shell). This encrypts all data between the machines.
- Don't run unnecessary services (called "daemons" in UNIX) that allow internet connections - some distributions turn these on by default. Examples are mail or news servers and printer daemon (lpd). If you want to see a list of the daemons running on your machine, at a command prompt type:
(You'll need to do this as "root" to get all process information). The lines that say "LISTEN" means a daemon is waiting for connections on the specified TCP port. Don't forget to check your UDP ports too - all sorts of things can lurk there.
- Firewall your machine using iptables(8) (or possibly ipchains(8) or even ipfwadm(8) if you're on an older machine). Don't just deny that which you know you don't want - deny everything, then specifically allow what you want to be let in.
See also SecuringYourBox (or refactor it to here.)
Application / General Encryption
GNU Privacy Guard (GPG) is an encryption program compatible with Pretty Good Privacy (PGP). It uses public-key cryptography, and many email clients have hooks that allow you to fairly easily encrypt and "sign" email. See our GPG/PGPNotes page.
Wireless Network Security: