Macslash has posted the short version of the Opener malware story, while Macintouch has a very detailed long version. Slashdot, of course, has the longest version of all (or at least, of all I've seen so far =).
If you are running Mac OS X (and especially, if you are new to Unix), thenaside from the advice outlined in the above sources, you should also take the time to learn and follow security best practices. The Macintouch piece links to a Corsaire white paper on Securing Mac OS X. Also useful are the ten-part Mac OS X Security series from MacWrite, and the O'Reilly MacDevCenter's Mac OS X Security Primer.