KentuckyFC writes: "Although quantum key distribution is unconditionally secure, the devices used to send quantum messages are inevitably imperfect. Last year, physicists used this weakness to hack a commercial quantum cryptography system. That led others to develop device-independent quantum protocols that would be immune from these problems. However, group of British physicists now say these attempts all treat quantum cryptography as if it is a single-shot process that uses the equipment only once. That overlooks the possibility that an adversary can program devices to store data in one protocol and leak it in subsequent protocols, in ways that are hard or impossible to counter. The only known way round this is to use the cryptographic gear only once but this solution is so costly that the physicists query whether it is generally practical. That looks like a serious fly in the ointment for those promising perfectly secure communication."