Tips for keeping your Macintosh or Linux computer safe.

Choose hard to guess passwords, with uppercase and lowercase characters, numbers and special signs. If you transfer files or do remote login, use an encrypted session, like ssh, scp, imaps instead of telnet, ftp, pop or imap. Thunderbird is a free imaps capable mail client, available at http://www.mozilla.org.

Keep your computer uptodate on patches. For Macintosh, see http://security.anu.edu.au/softwareupdate.

Turn off unnecessary services. You can check with "netstat -a", on what ports your machine is listening on the network. If you don't need to log into your computer from a remote machine, turn sshd off. On a Macintosh this is done under the System Preferences window, click on Sharing under Internet & Network and deselect sshd. If you need to login remotely, here are some tips to make it less vulnerable to ssh brute force password guessing attacks: http://www.ducea.com/2006/06/28/using-iptables-to-block-brute-force-attacks/ and
http://www.macosxhints.com/article.php?story=20050815135941513&lsrc=osxh.

Run a firewall. Iptables on Linux can do very sophisticated access control, TCPWrappers are less comprehensive but easier to use. To activate the firewall in MacOS X: On the System Preferences window, click on Sharing under Internet & Network. Click on the Firewall tab, and click Start.

Always make sure that you have the newest browser version.

Back up your data.