multiple compromised systems flood the bandwidth or resources of a targeted system, usually one or more web servers.
Check CERT and some of the other top level results:
http://www.google.com/search?hl=en&q=denialof+service&aq=0&oq=Denial+of
If it was YOU doing the DOS attack, outbound, but it isn't, it is inbound from the hordes of botnets. No where did Wiki say the target system (yours) is infected. My guess is the only thing it can do to OS X systems is make it next to impossible to do anything else, which is what happens.
All you can do is harden your router, block the source at the time (for which NetBarrier would work) or a "smart" router (mine I don't know if it puts an IP into a 30 minute "penalty" block list, but it might).
The best tool I can think of is the demo of Intego VirusBarrier and NetBarrier.
Security Threats:
Discovered: January 27, 2009
Updated: January 27, 2009 7:51:16 PM
Also Known As: OSX/iWorkS-B [Sophos], OSX/IWService.b [McAfee]
Type: Trojan
Infection Length: 413,604 bytes
OSX.Iservice.B is a Trojan horse that runs on Mac OS X and opens a back door on the compromised computer.
http://www.symantec.com/business/security_response/writeup.jsp?docid=2009-012620 -2836-99