The first attack that claimed to be able to eavesdrop the whole key without leaving any trace was demonstrated in 2010. It was experimentally shown that the single-photon detectors in two commercial devices could be fully remote-controlled using specially tailored bright illumination. In a spree of publications thereafter, the collaboration between the Norwegian University of Science and Technology in Norway and Max Planck Institute for the Science of Light in Germany, has now demonstrated several methods to successfully eavesdrop on commercial QKD systems based on weaknesses of Avalanche photodiodes (APDs) operating in gated mode. This has sparked research on new approaches to securing communications networks.