I don't remembered the details, but I do remember that the virus could get out the the net because of that / being in the wine config.
How did that work? I can't think of anything whatsoever that a win32 program under emulation could do with ro access to / - it can't run ELF apps, it can't write, it can't understand the format of the config files even!
So having / in the default config file is a very very bad idea, because these problems could happen again in the future.
The solution is for people not to use mail apps that implicitly trust any local software which gives them email, not to annoy and frustrate users of Wine for no obvious reason. As I've already said, I'd need strong proof that having / mapped allowed viruses to spread more easily before I'd accept this argument.
BTW I've added binaries and source of winesetuptk to the wine sourceforge page, the license is gpl.
Cool :)