Like the Meltdown bug, the Spectre bug is a hardware bug in the form of a CPU design flaw. Unlike the Meltdown bug which only affects Intel processors, the Spectre bug impacts Intel, AMD, and some ARM (used in many smart phones and other mobile devices) processors. These three are by far the most common CPUs on the planet, running literally billions of devices. In a Spectre attack, the CPU is tricked into executing instructions that it normally would not, causing leaks in the victims memory address space.