On Thu, 15 Apr 1999, John Fulmer wrote:

> Viruses usually exploit the fact there is no user access controls on
> Win98,and earlier and Macintosh.
> 
> With user access controls, it is much harder to infect system files, and
> you would have to rely more on bugs. I guess virus coders think it's not
> worth the hassle. 

That's part of it. The other part is the open source model. On the
POSIX systems, there are more people finding theoretical security
holes, and closing them, than there are people expoiting them. On the
other hand, a handful of people in Redmond have complete
responsibility for security on one of the OS's you mentioned; anyone
else who's interested in such matters can only satisfy that interest
by writing viruses.