Malicious Software

Agax
An expandable free Mac antivirus program by John Dalgliesh. It offers both standard virus-scanning facilities and more advanced background protection, so you don't get infected in the first place.
http://www.defyne.org/agax/

The Code 9811 Virus
On the encounter with an uncommon Macintosh computer virus, its symptoms and how to get rid of it.
http://www.silent.se/9811

Mac Virus
Macintosh antivirus news, advisories, downloads and reviews of mac virus scanners and definitions of viruses and trojans for Mac OS and Mac OS X.
http://www.macvirus.org/

Nimda spreads via Samba Services
Example/Logs of Nimda virus/worm in action on Mac OS X server Samba Service.
http://www.securemac.com/macosxnimdasamba.php

Norton AntiVirus for Macintosh
Provides real time malware protection, scanning and removal. Can be configured to scan email and external storage devices when they are mounted.
http://www.symantec.com/nav/nav_mac/

Tracker, DelProtect, and Scanner
These antivirus utilities by Ioannis Galidakis are meant to track down 68K viruses on your system. They MAY prove to be useful, if you are unable or unwilling to purchase professional commercial antivirus software, or in conjunction with such software.
http://users.forthnet.gr/ath/jgal/programming/index.html

Vaccine
A free HyperCard virus utility written by Bill Swagerty that will inspect all the stacks on your hard drive, or any part of it, for most HyperCard viruses.
http://www.hyperactivesw.com/Virus2.html

VirusBarrier
Complete antivirus software suite for the Macintosh to eliminates all known viruses including system and macro viruses. Supports archive scans
http://www.intego.com/virusbarrier/