[IP] Viruses
Begin forwarded message:
From: Spafford Gene <spaf@xxxxxxxxxxxxxxxxx>
Date: May 20, 2005 10:47:23 PM EDT
To: David Farber <dave@xxxxxxxxxx>
Subject: Viruses
Basically, any system that has writable store that can allow written  
files to be executed, and which does not run mandatory access control  
(MAC) according to an appropriate integrity policy (ala the Biba  
model), can be infected by a virus.
The Mac OS X does not use MAC and policies such as Biba.  Therefore,  
it can support a virus.
It is trivial to write a virus for Unix.   Back in 1989, two articles  
were published in the (now defunct) journal  "Computing  
Systems" (Volume 2, Number 2, Spring, 1989)  that described Unix  
viruses.  The articles were by Tom Duff and Doug McIlroy.   Doug's  
article, "Virology 101" is available in many places on the WWW; I  
didn't find a copy of Tom's in a cursory search.
Linux viruses have been written and published.
Now, more to the point is how easy is it to craft a virus that is  
appropriately stealthy and also will spread reasonably well?  Those  
are more difficult issues to address rather than simply writing  
something that can replicate. This may be where the Mac OS has some  
defensive advantages.
However, there is no question that viruses can be written for Mac OS  
or any other standard Unix-like system.
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