In those good old easy-to-manage pre-mobility days, personal computers presented few actual threats to a network. Sure, there was the occasional virus you’d get from a borrowed floppy disk, but the rate, or at least the speed, of infection was pretty low—limited substantially by the low bandwidth and high latency of "sneakernet" technology. In those days, computers were bulky behemoths that squatted on desks and never moved. They were secure because the network was secure, if there was one at all.
Alas, those halcyon days are behind us now, relegated to the dustbin of history. And indeed they should be. Mobile computers are wonderful! We can work, well, just about anywhere, slay monsters anywhere, play solitaire anywhere. The true advance, of course, was the combination of mobility and a network connection. Got 10 minutes? Haul out the laptop and check that e-mail. Who needs an office anymore?
Of course, Murphy never gets to rest. It seems that with every technological advance (that’s a euphemism for "another way your employer squeezes more work out of you"), there’s a dark side. Connected mobility’s dark side is the ease with which unscrupulous people can wreak havoc across an entire network.
Armed with a portable computer that’s routinely connected to multiple public networks, out-of-date machines operated by people with an "I don’t really care" attitude are the most dangerous thing I can envision. And when "I don’t really care" then wants to connect back to his corporate network, need I really describe the resulting carnage? Indeed, this exact scenario is arguably one of the fastest-growing infection vectors imaginable.