Is Linux is virus free? The author of foobar blog provides some insight about the same. Linux users can't just catch a virus by email or downloading malware from the Internet, contrary to "those Windows users".
From the foobar blog post:
Then you save an email attachment under Linux, the execute flag is normally NOT set and thus, the file can't be executed just by clicking on it. So, no luck?
Not so fast. Modern desktop environments, such as Gnome and KDE, conveniently offer a nice "workaround" called 'launchers'. Those are small files that describe how something should be started. Just a few lines that specify the name, the icon that should be displayed and the actual command to execute. Conveniently, the syntax of those launcher files is the same for Gnome and KDE. And those launchers don't have to have any execute permissions set on them! Desktop environments treat those files as a special case, so when you click on them Gnome or KDE will happily execute the command that was specified within the launcher description and without the need for the execute bit to be set on the launcher itself. Now we are getting somewhere!
Sure Linux is bit secure out of box, but Linux desktop is all together different thing. It is just matter of time, once Linux got popular crackers will target Linux desktop too (think of all those netbooks loaded with Linux). Right now there is not much protections for normal user account and users who will foolishly click on something in an email with attachments. However, SELinux or AppArmor may be used to protect the system.
Read more: How to write a Linux virus in 5 easy steps