^^
Note to new Linux users: No antivirus needed
http://www.linux.com/feature/60208
also,i dont think Linux virus/trojans will get a hold if the platform become very popular.because,Linux inherently have a better system wide permission system,which is very hard to break.may be a binary injection(elf-32) or sudo/SUID vulnerability which should be checked.otherwise,there is no fear of virus even after 10 yrs!
Use sxid(sudo apt-get install sxid) tool and schedule cron to run it to find any unwanted SUID's set
also,rootkits are what any os shud fear.in Linux also,we cannot easily find the presence of rootkits(which is rare and only server admins shud take care of!) .although tools like rkhunter,chkrootkit exists!install these,if ur paranoid.