According to news reports, the U.S. government's electronic spy agency has developed technology to penetrate targeted computers, even if they are not connected to the Internet.
The New York Times says for at least five years the National Security Agency has been secretly implanting tiny electronic circuits capable of transmitting data on covert radio channels.
Briefcase-sized relay stations can pick up those signals kilometers away and transmit them to the spy agency's headquarters.
According to the reports, the new technology solved the problem of accessing computers that U.S. adversaries tried to make impenetrable.
Sometimes the circuits were hidden in cables used for connecting computers to peripheral devices, such as keyboards or speakers. The hardware was mostly implanted by U.S. spies, but sometimes by manufacturers or unwitting users.
The spying hardware and software can stay active for years without being detected. It can be turned on or off remotely, acting as digital sleeper cells' to be activated as needed.
Government and military agencies around the world, as well as private companies, employ computer software called firewalls' to prevent unauthorized access. But all spy agencies try to develop software that can breach those walls.
The German newsmagazine Der Spiegel says it had access to a 50-page NSA document listing software that can survive reboots and upgrades in targeted computers, securing permanent access to their networks.
According to Der Spiegel, many of those weapons are remotely installable over the Internet while others require direct access to the device.