05-25-2009, 11:23 PM
The only ways a Mac could "host" a windows virus, that I know of
(I am not an OSX expert, this is just from things I've read and researched):
1) Somehow are using a darwine based install of a windows software package that has a virus where it would try to propagate outside of your system (rare, but possible - happens more often to those running outlook or IE under darwine or crossover).
2) You run some sort of virtual machine (parallels, virtualbox, vmware fusion) with a windows install that gets a virus so whenever that VM is running, it's possible for the virus to spread to other windows machines.
3) Not really propagate, but you forward an email onto someone that contains a windows virus - might call it manual propagation since you had to manually forward it on.
4) You have dual booted into windows (via bootcamp) and have a virus on your bootcamp partition.
5) Certain macro virus' on certain versions of microsoft products could propagate a virus - I think this is broken in Office '08 since vbscript is not available in that release of office, but I could be wrong (ie: if there is a macro virus that doesn't depend on vbscript).
6) You open up a file share area on your mac, and someone stores an infected file on your computer that other people copy off of your share (not really you propagating, more just it being shared and other people taking the file and infecting themselves - I could see this happening with someone sharing an illegal download)
The chance of you propagating a windows virus via a Mac is very slim - I'm not saying it's impossible, but it's slim.