The trouble with all this Linux / M$ bashing is that really it's pretty irrelevant...
Yes M$ has problems and yes the open source community has the potential to fix security problems in less time than M$ does. But really - if Linux out-numbered M$ on the desktop then there would be more people trying to hack Linux boxes and more exploits found and less people doing the same for M$. And IMO M$ have gotten a lot better recently - 2K, XP and 2003 server are much better than their earlier attempts and the kind of exploits we're getting now seem more advanced. Forget e-mail / script viruses - those started out as M$'s fault - they really were wide open - but now are down to the user... Honestly if any company out there doesn't have suitable security measures (AV, firewall, user training, etc) then they deserve whatever they get IMO. How many viruses have I ever been infected with? None. How many worms / hacks have gotten through my firewall? None (to my knowledge!)... I'm not saying it isn't possibly but most attacks are from worms / scanners and if you leave yourself that open then you've only got yourself to blame. Blocking / detecting targetted attacks from knowledgeable hackers if always going to be hard no matter what you are running...
Anyway I'm ranting so I'll get my coat!