Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
In our cosy *nix world we don't suffer from viruses, or rather we didn't. But thanks to an amazing piece of reverse engineering we have SAMBA, and SAMBA allows Windows machines to talk to Linux (and Solaris) networks and store files on them.
What this means is that we can have viruses by proxy if any Linux network we deploy has Windows workstations... which mostly they do. Often on the same network, thanks to the magic of that other unifying technology Open LDAP there are Linux and Mac workstations too.
Of course the Linux servers and the Mac/Linux desktops are immune to Windows viruses.