Without viruses and other malware, Linux is typically much harder for the average user to mess up. But if you are setting up a GNOME desktop for someone who seems to do things like delete the window list, or for public use, then you should lock down the desktop.
Pessulus is a graphical lockdown editor for GNOME. Instead of finding and changing individual GNOME gconf settings, you can use Pessulus to easily access the most important settings for locking down GNOME.
Install Pessulus from the package pessulus (click the link to install), or by running the command below in your terminal: