The concept represents nearly the maximum protection one network can have from another (save turning the device off). One way to transfer data between the outside world and the air-gapped system is to copy data on a removable storage medium such as a removable disk or USB flash drive and physically carry the storage to the other system. This access still has to be carefully controlled since USB drive may have vulnerabilities (see below). The upside to this is that such a network can generally be regarded as a closed system (in terms of information, signals, and emissions security), unable to be accessed from the outside world. The downside is that transferring information (from the outside world) to be analyzed by computers on the secure network is extraordinarily labor-intensive, often involving human security analysis of prospective programs or data to be entered onto air-gapped networks and possibly even human manual re-entry of the data following security analysis. That's why another way to transfer data, used in appropriate situations like critical industries, is to use data diodes and electronic airgaps, that assure a physical cut of the network by a specific hardware. Sophisticated computer viruses for use in cyberwarfare, such as Stuxnet and agent.btz have been designed to infect air-gapped systems by exploiting security holes related to the handling of removable media. The possibility of using acoustic communication has also been demonstrated by researchers. Researchers have also demonstrated the feasibility of data exfiltration using FM frequency signals. Examples Examples of the types of networks or systems that may be air gapped include: Military/governmental computer networks/systems; Financial computer systems, such as stock exchanges; Industrial control systems, such as SCADA in Oil & Gas fields; National and state lottery game machines or random number generators, which are required to be completely isolated from networks to prevent lottery fraud Life-critical systems, such as: Controls of nuclear power plants; Computers used in aviation, such as FADECs, air traffic control systems, and avionics; Computerized medical equipment; Very simple systems, where there is no need to compromise security in the first place, such as: The engine control unit and other devices on the CAN bus in an automobile; A digital thermostat for temperature and compressor regulation in home HVAC and refrigeration systems; Electronic sprinkler controls for watering of lawns. Many of these systems have since added features that connect them during limited periods of time to the