The paper discusses a method to hack commercially available quantum key distribution (QKD) systems using tailored bright illumination. The authors demonstrate that the detectors in two commercial QKD systems, Clavis2 and QPN 5505, can be fully controlled by classical laser pulses superimposed on bright continuous-wave (CW) illumination. This allows Eve to blind the gated detectors, converting them into classical, linear detectors that measure the bit values sent by Alice with matching or incompatible bases. The attack is feasible for most QKD systems using avalanche photodiodes (APDs) and can be implemented with off-the-shelf components. The authors propose a plug-and-play eavesdropper based on this technique and suggest that addressing such vulnerabilities is crucial for enhancing the security of practical QKD systems. They have notified the manufacturers, ID Quantique and MagiQ Technologies, and ID Quantique has implemented countermeasures.The paper discusses a method to hack commercially available quantum key distribution (QKD) systems using tailored bright illumination. The authors demonstrate that the detectors in two commercial QKD systems, Clavis2 and QPN 5505, can be fully controlled by classical laser pulses superimposed on bright continuous-wave (CW) illumination. This allows Eve to blind the gated detectors, converting them into classical, linear detectors that measure the bit values sent by Alice with matching or incompatible bases. The attack is feasible for most QKD systems using avalanche photodiodes (APDs) and can be implemented with off-the-shelf components. The authors propose a plug-and-play eavesdropper based on this technique and suggest that addressing such vulnerabilities is crucial for enhancing the security of practical QKD systems. They have notified the manufacturers, ID Quantique and MagiQ Technologies, and ID Quantique has implemented countermeasures.