Your once reliable mobile phone suddenly freezes. The keypad no longer functions, and it cannot make or receive calls or text messages. You try to power off, but nothing happens. You remove the battery and reinsert it; the phone simply returns to its frozen state. Clearly, this is no ordinary glitch. Hours later you learn that yours is not an isolated problem: millions of other people also saw their phones suddenly, inexplicably, freeze.
This is one possible way that we might experience a large-scale hardware attack—one that is rooted in the increasingly sophisticated integrated circuits that serve as the brains of many of the devices we rely on every day. These circuits have become so complex that no single set of engineers can understand every piece of their design; instead teams of engineers on far-flung continents design parts of the chip, and it all comes together for the first time when the chip is printed onto silicon. The circuitry is so complex that exhaustive testing is impossible. Any bug placed in the chip’s code will go unnoticed until it is activated by some sort of trigger, such as a specific date and time—like the Trojan horse, it initiates its attack after it is safely inside the guts of the hardware.