In the todays Linux news there was an Article about the “Hand of Thief” Trojan analyzed by Avast. What makes this Trojan special is that it’s crafted for Linux – read more at http://blog.avast.com/2013/08/27/linux-trojan-hand-of-thief-ungloved/
A first step to prevent from manifesting itself in the system is to mark your Home directory “noexec”. With this little trick you can prevent applications from being launched directly from within your home-directory (which should be the only place where your user has write privileges in addition to /tmp). To do so, add the parameter “noexec” to the corresponding /etc/fstab entry.
Hopefully you have your /home on a different filesystem :-)