if you are worried about the current trojan news (and dont be unless your a) a perv and b) stupid enough to install something dodgy from a porn site with your root password, then this macworld article is quite interesting and informative to the layman.
http://www.macworld.com/2007/10/firstlooks/trojanhorse/index.php?lsrc=mwrss
http://www.macworld.com/2007/10/firstlooks/trojanhorse/index.php?lsrc=mwrss