William Stearns has a good write up on Linux security tips for first time Linux users.
Here are a few:
- Set up regular updates for your particular Linux distribution
- Lock your system when you step away from it. To lock the Gnome graphical desktop, run the following command, part of the “gnome-screensaver” package:gnome-screensaver-command –lockFrom a text console, run this, part of the vlock package:vlock -aFor KDE, right click on the desktop and select “Lock Session”. In Ubuntu, press Ctrl-Alt-l (the letter “Ell”, configurable in System/Preferences/Keyboard shortcuts). All require the password of the logged-in user to continue work.
- Do your day-to-day work with a non-root account. When you need to do root-level tasks, become root with “sudo” or “su” long enough to do the task (alternately, log in as root on a text console for this task). http://www.stearns.org/doc/sudo.current.html
Go check out the rest of the tips.