It's no secret that computers are insecure. The risks are about to get worse, because computers are being embedded into physical devices and will affect lives, not just our data. Many of today's new computers are not just screens that we stare at, but objects in our world with which we interact. A refrigerator is now a computer that keeps things cold; a car is now a computer with four wheels and an engine. These computers sense us and our environment, and they affect us and our environment. They talk to each other over networks ... and they have physical agency. They drive our cars, pilot our planes, and run our power plants. They control traffic, administer drugs ... and dispatch emergency services. These connected computers and the network that connects them - collectively known as the internet of things" - affect the world in a direct physical manner. Computers fail differently than most other machines: It's not just that they can be attacked remotely - they can be attacked all at once. It's impossible to take an old refrigerator and infect it with a virus or recruit it into a denial-of-service botnet, and a car without an internet connection simply can't be hacked remotely. But that computer with four wheels and an engine? It - along with all other cars of the same make and model - can be made to run off the road, all at the same time. Do we want to allow vulnerable automobiles on the streets and highways during the weeks before a new security patch is written, tested, and distributed?