Mac V Vista security.

I still wonder why none of those security gurus ever say that connecting several million computers with one network is a bad idea to start with. Or would that put them out of business?

More than that, it would go against their earlier statements. Having a mix of OSes is sort of like having a mix of DNA. If only a fraction of the computers can be taken out by a given virus, the rest will continue to operate after an attack.

There are lots of things they warn you about in the security of Linux. In most cases it only takes a little thinking to see why the bad ideas are bad. For example, you have to be careful about setting up NFS. You don't want "root" on another machine to get to act as "root" on yours etc.

Because it's impossible to put that genie back in the bottle?

I don't think the number of "widgets" connected to a network correlates that much with a lack of security anyway. Look at cell phones -- millions of them exist, and although, sure, an individual phone model may be hackable to, e.g., retrieve the address book, the network itself utilitizes protocols that have generally remained unhacked for over a decade now (i.e., no one's reporting the ability to place free phone calls).