Quantum is the codename of a secret program of the National Security Agency (NSA) that can monitor offline computers. The NSA can access computers through radio waves emitted from a variety of customized devices. One device, nicknamed "Cottonmouth I," is a modified USB card containing a tiny radio transceiver that can secretly transmit and receive data to and from the computer.
The NSA also uses tiny circuit boards installed into laptop computers that broadcast to the agency even when the computer is completely not connected to the Internet. These circuit boards communicate with a briefcase-sized relay station that the NSA calls "Nightstand." Nightstand can attack a computer from as far as eight miles away and insert packets of data.